Trading Assets and Liabilities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading assets	$ 22,099		$ 28,894
US Government sponsored enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading assets	97	[1]	159	[1]
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] | US Government sponsored enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading assets	97		133
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member] | US Government sponsored enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading assets	$ 0		$ 26

[1] Includes mortgage backed securities of $97 million and $133 million issued or guaranteed by the Federal National Mortgage Association ("FNMA") and $0 million and $26 million issued or guaranteed by the Federal Home Loan Mortgage Corporation ("FHLMC") at September 30, 2014 and December 31, 2013, respectively.