Trading Assets and Liabilities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Derivatives included in trading assets, amount offset	$ 4,811	[1],[2]	$ 3,870	[1],[2]
Derivatives included in trading liabilities, amount offset	1,724	[1],[2]	2,116	[1],[2]
Trading Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Derivatives included in trading assets, amount offset	4,811		3,870
Trading Liabilities [Member]
Schedule of Available-for-sale Securities [Line Items]
Derivatives included in trading liabilities, amount offset	$ 1,724		$ 2,116

[1] Netting is performed at a counterparty level in cases where enforceable master netting and credit support agreements are in place, regardless of the type of derivative instrument. Therefore, we have not attempted to allocate netting to the different types of derivative instruments shown in the table above.

[2] Represents the netting of cash collateral posted and received by counterparty under enforceable credit support agreements.