Accumulated Other Comprehensive Income (Loss) - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on net unrealized gains (losses) arising during period	$ (27)	$ 26	$ (201)	$ 312
Tax on reclassification adjustment	(1)	(13)	(12)	(27)
Tax on reversal of provision for credit losses realized in net income (loss)	0	(1)	0	(1)
Tax on amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity realized in net income (loss)	1	4	3	6
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	3	(13)	3	33
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	(1)	(4)	(7)	24
Tax on reclassification adjustment	(1)	1	(2)	3
Pension and Postretirement Benefit Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on net unrealized gains (losses) arising during period	$ 0	$ (1)	$ 1	$ (1)
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