Trading Assets and Liabilities - Additional Information (Detail) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Derivatives included in trading assets, amount offset	[1],[2]	$ 3,166	$ 4,480
Derivatives included in trading liabilities, amount offset	[1],[2]	4,178	3,823
Trading Assets [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivatives included in trading assets, amount offset		2,472	3,423
Trading Liabilities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivatives included in trading liabilities, amount offset		$ 4,058	$ 3,680

[1] Netting is performed at a counterparty level in cases where enforceable master netting agreements are in place, regardless of the type of derivative instrument. Therefore, we have not allocated 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 netting agreements.