Accumulated Other Comprehensive Income (Loss) - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on net unrealized gains (losses) arising during period	$ 298	$ 145	$ (68)
Tax on reclassification adjustment	(33)	(21)	(6)
Tax on reversal of provision for credit losses realized in net income (loss)	(1)
Tax on amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity realized in net income (loss)	8	4	4
Unrealized Gains (Losses) on Fair Value Option Liabilities Attributable to Our Own Credit Spread [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on net unrealized gains (losses) arising during period	8	(68)	103
Tax on reclassification adjustment		(30)
Unrealized Gains (Losses) on Derivatives Designated as Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on net unrealized gains (losses) arising during period	20	(5)	7
Tax on reclassification adjustment	3	8	5
Pension and Postretirement Benefit Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on net unrealized gains (losses) arising during period	$ (1)	(5)	$ 3
Accounting Standards Update 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on cumulative effect adjustment		$ 1