Trading Assets and Liabilities - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Derivatives included in trading assets, amount offset	[1],[2]	$ 4,079	$ 3,683
Derivatives included in trading liabilities, amount offset	[1],[2]	3,377	4,390
Dividend income on equity securities held for trading		78	37	$ 1
Trading Assets [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivatives included in trading assets, amount offset		2,763	2,538
Trading Liabilities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivatives included in trading liabilities, amount offset		$ 3,377	$ 4,351

[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.