Accumulated Other Comprehensive Income (Loss) - (Detail) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity						$ 17,026
Balance at end of period, common equity		$ 16,972		$ 17,075		16,972		$ 17,075
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity		81		830		679		(277)
Balance at end of period, common equity		(3)		834		(3)		834
Accumulated Other Comprehensive Loss [Member] | As Previously Reported [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity						679		(279)
Balance at end of period, common equity				834				834
Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity		172				750		(114)
Net unrealized gains (losses) arising during the period, net of tax		(86)		84		(636)		990
Reclassification adjustment for (gains) losses realized in net income (loss)		(3)	[1]	(39)	[1]	(39)	[2]	(84)	[2]
Reversal of provision for credit losses realized in net income (loss), net of tax	[1]	0		(1)		0		(1)
Amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity realized in net income (loss), net of tax	[3]	3		12		11		19
Total other comprehensive income (loss) for period		(86)		56		(664)		924
Balance at end of period, common equity		86				86
Unrealized Gains (Losses) on Investment Securities [Member] | As Previously Reported [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity				754				(116)
Balance at end of period, common equity				810				810
Unrealized Gains (Losses) on Investment Securities [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Accounting Standards Update 2016-13 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity	[4]							2
Unrealized Gains (Losses) on Fair Value Option Liabilities Attributable to Our Own Credit Spread [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity		15		137		15		(9)
Net unrealized gains (losses) arising during the period, net of tax		9		(40)		9		106
Total other comprehensive income (loss) for period		9		(40)		9		106
Balance at end of period, common equity		24		97		24		97
Unrealized Gains (Losses) on Derivatives Designated as Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity		(100)		(58)		(79)		(151)
Net unrealized gains (losses) arising during the period, net of tax		(2)		(10)		(21)		75
Reclassification adjustment for (gains) losses realized in net income (loss)	[5]	(5)		0		(7)		8
Total other comprehensive income (loss) for period		(7)		(10)		(28)		83
Balance at end of period, common equity		(107)		(68)		(107)		(68)
Pension and Postretirement Benefit Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity		(6)		(3)		(7)		(3)
Net unrealized gains (losses) arising during the period, net of tax		0		(2)		1		(2)
Total other comprehensive income (loss) for period		0		(2)		1		(2)
Balance at end of period, common equity		$ (6)		$ (5)		$ (6)		$ (5)

[1] Changes in the allowance for credit losses on securities available-for-sale are included in the provision for credit losses in our consolidated statement of income (loss).

[2] Amount reclassified to net income (loss) is included in other securities gains, net in our consolidated statement of income (loss).

[3] Amount amortized to net income (loss) is included in interest income in our consolidated statement of income (loss). During 2014, we transferred securities from available-for-sale to held-to-maturity. At the date of transfer, AOCI included net pretax unrealized losses related to the transferred securities which are being amortized over the remaining contractual life of each security as an adjustment of yield in a manner consistent with the amortization of any premium or discount.

[4] See Note 2, "Summary of Significant Accounting Policies and New Accounting Pronouncements," in our 2020 Form 10-K for additional discussion.

[5] Amount reclassified to net income (loss) is included in net interest income in our consolidated statement of income (loss).