Trading Assets and Liabilities - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt and Equity Securities, FV-NI [Line Items]
Derivatives included in trading assets, amount offset	[1],[2]	$ 4,360		$ 4,079
Derivatives included in trading liabilities, amount offset	[1],[2]	1,953		3,377
Dividend income on equity securities held for trading		26	$ 26
Trading Assets [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivatives included in trading assets, amount offset		2,862		2,763
Trading Liabilities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivatives included in trading liabilities, amount offset		$ 1,953		$ 3,377

[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.