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Cash and Securities Segregated Under Federal Regulations and Other Requirements (Details) (USD $)
Dec. 31, 2011
Dec. 31, 2010
Cash and Securities Segregated Under Federal Regulations and Other Requirements [Abstract]    
United States Treasury Bills in special reserve bank custody account for exclusive benefit of brokerage customers of SCB LLC $ 1,200,000,000 $ 1,100,000,000
Restricted funds held for benefit of customers by AllianceBernstein Investments, Inc. $ 39,900,000 $ 25,300,000