Standard & Poor's implemented a sweeping overhaul of its rating criteria on Tuesday that resulted in a downgrade on 15 big banking companies, including the world's last AAA-rated bank. Could this be the end of the AAA era?

S&P announced earlier this month that it will gradually apply the new ratings for more than 750 banking companies worldwide, starting with the largest.

JPMorgan Chase, Bank of America, Citigroup, Wells Fargo, Goldman Sachs Group, Morgan Stanley, Barclays, HSBC Holdings, and UBS, were among the banks that had their ratings reduced by one notch each. A notch is one third of a letter rating, reports CNBC.

On the upside, S&P left the ratings of 20 banks as they were and raised the ratings of two. But even this was worse than S&P expected. Indeed, "S&P officials said earlier this month they expected about 20 percent of all banks would see their ratings drop, while 20 percent would get higher ratings and 60 percent would stay the same."

Still, other smaller banks have yet to put themselves at the mercy of S&P's new rating system.

Rabobank -- Last to fall
Rabobank was the last to lose its stellar AAA rating, which fell to two notches to an AA rating. As Reuters puts it, "the global banking crisis finally caught up."

For Rabobank, the AAA rating had been a source of pride. Surely the steep downgrade must have felt a low blow, but Rabobank can take solace in the fact that it is still the highest rated privately owned bank in the world, according to S&P. The bank also maintains, for now, its AAA rating from Moody's. Fitch rates it AA+.

Implications
S&P's new rating system is part of an attempt to repair the agency's reputation after wrongly slapping AAA ratings on securities backed by subprime mortgages.

"S&P did not say it literally, but they communicated that a bank can no longer have a triple-A rating," Rabobank's Chief Financial Officer Bert Bruggink told Dutch TV program RTL Z on Wednesday. "Nothing is risk free. Even the best countries prove not to be risk free. In that respect, I think S&P's conclusion is a right one." (via Reuters)

Investing ideas
As demonstrated, banks have something to fear from the new rating system. But S&P says they expect 20% of banks to get higher ratings under this system. This could lead to some positive market response for those that do receive higher ratings.

To get ideas about which financial companies may benefit from a new rating system we decided to create a screen of financial stocks that have recently experienced a significant increase of institutional buying.

The smart money seems to think these companies have more of an upside than downside. Do you agree?

List sorted alphabetically. (Click here to access free, interactive tools to analyze these ideas.)

1. Brandywine Realty Trust (NYSE: BDN): Brandywine Realty Trust is a publicly owned real estate investment firm. Market cap of $1.14B. Net institutional shares purchased over the current quarter at 15.9M, which is 11.93% of the company's 133.26M share float. This is a risky stock that is significantly more volatile than the overall market (beta = 2.18). The stock is a short squeeze candidate, with a short float at 9.97% (equivalent to 5.7 days of average volume). The stock has performed poorly over the last month, losing 10.7%.

2. Encore Capital Group (Nasdaq: ECPG): Engages in consumer debt buying and recovery business. Market cap of $510.83M. Net institutional shares purchased over the current quarter at 1.2M, which is 9.73% of the company's 12.33M share float. This is a risky stock that is significantly more volatile than the overall market (beta = 2.2). Might be undervalued at current levels, with a PEG ratio at 0.64, and P/FCF ratio at 6.84. The stock has performed poorly over the last month, losing 22.98%.

3. EastGroup Properties (NYSE: EGP): Focuses on the development, acquisition, and operation of industrial properties in the United States. Market cap of $1.10B. Net institutional shares purchased over the current quarter at 2.8M, which is 10.87% of the company's 25.76M share float. The stock is a short squeeze candidate, with a short float at 6.89% (equivalent to 7.78 days of average volume). The stock has gained 6.73% over the last year.

4. Enstar Group Limited (Nasdaq: ESGR): Enstar Group Limited, through its subsidiaries, acquires and manages insurance and reinsurance companies in run-off. Market cap of $1.37B. Net institutional shares purchased over the current quarter at 878.0K, which is 10.96% of the company's 8.01M share float. The stock has gained 14.28% over the last year.

5. Financial Engines (Nasdaq: FNGN): Financial Engines, and its subsidiaries provide independent, technology-enabled portfolio management services, investment advice, and retirement income services to participants in employer-sponsored defined contribution plans, such as 401(k) plans. Market cap of $919.10M. Net institutional shares purchased over the current quarter at 5.8M, which is 13.33% of the company's 43.50M share float. The stock is a short squeeze candidate, with a short float at 20.76% (equivalent to 20.53 days of average volume). The stock has performed poorly over the last month, losing 16.18%.

6. HFF (NYSE: HF): Provides commercial real estate and capital markets services to the commercial real estate industry in the United States. Market cap of $372.39M. Net institutional shares purchased over the current quarter at 3.4M, which is 11.93% of the company's 28.51M share float. This is a risky stock that is significantly more volatile than the overall market (beta = 2.44). The stock has performed poorly over the last month, losing 11.84%.

7. Knight Capital Group (NYSE: KCG): Provides access to the capital markets across multiple asset classes to buy-and sell-side firms, and corporations, as well as offers capital markets services to corporate issuers and private companies primarily in the United States. Market cap of $1.16B. Net institutional shares purchased over the current quarter at 8.6M, which is 9.68% of the company's 88.87M share float. Relatively low correlation to the market (beta = 0.26), which may be appealing to risk averse investors. The stock has lost 10.43% over the last year.

8. Symetra Financial (NYSE: SYA): Operates as a financial services company in the life insurance industry in the United States. Market cap of $1.04B. Net institutional shares purchased over the current quarter at 15.8M, which is 13.21% of the company's 119.58M share float. The stock has recently rebounded, and is currently trading 6.5% above its SMA20 and 7.19% above its SMA50. However, the stock still trades -18.59% below its SMA200. The stock has performed poorly over the last month, losing 11.95%.

9. UDR (NYSE: UDR): Operates as a self-administered equity real estate investment trust (REIT). Market cap of $4.95B. Net institutional shares purchased over the current quarter at 28.7M, which is 13.35% of the company's 214.93M share float. The stock has gained 4.77% over the last year.

10. Walter Investment Management (NYSE: WAC): Operates as a mortgage portfolio owner and mortgage servicer, specializing in sub prime, non-conforming, and other credit challenged residential loans primarily in the southeastern United States. Market cap of $572.24M. Net institutional shares purchased over the current quarter at 2.5M, which is 10.28% of the company's 24.32M share float. The stock is a short squeeze candidate, with a short float at 5.82% (equivalent to 5.69 days of average volume). The stock has had a couple of great days, gaining 5.12% over the last week. The stock has performed poorly over the last month, losing 14.95%.

Interactive Chart: Press Play to compare changes in analyst ratings over the last two years for the stocks mentioned above. Analyst ratings sourced from Zacks Investment Research.

Kapitall's Rebecca Lipman does not own any of the shares mentioned above. Institutional data sourced from Fidelity. All other data sourced from Finviz.