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Investment Securities - Schedule of Outstanding Contractual Balance and Carrying Value of Acquired Credit-Impaired Debt Securities (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Outstanding Balance and Carrying Value of Acquired Securities    
Contractual principal and interest $ 4,366 $ 4,700
Carrying value 2,923 2,896
Amortized cost $ 2,413 $ 2,432