Accumulated Other Comprehensive Income - (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity		$ 17,026
Balance at end of period, common equity		16,709	$ 17,054
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity		679	(277)
Balance at end of period, common equity		26
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			978
Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity		750	(114)
Net unrealized gains (losses) arising during the period, net of tax		(613)	775
Reclassification adjustment, net of tax	[1]	(22)	(21)
Provision for credit losses realized in net income (loss), net of tax	[2]	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]	4	3
Total other comprehensive income (loss) for period		(631)	758
Balance at end of period, common equity		119
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		750	(116)
Balance at end of period, common equity			644
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			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	(9)
Net unrealized gains (losses) arising during the period, net of tax		(10)	407
Total other comprehensive income (loss) for period		(10)	407
Balance at end of period, common equity		5	398
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		(79)	(151)
Net unrealized gains (losses) arising during the period, net of tax		(13)	85
Reclassification adjustment, net of tax	[4]	1	5
Total other comprehensive income (loss) for period		(12)	90
Balance at end of period, common equity		(91)	(61)
Pension and Postretirement Benefit Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period, common equity		(7)	(3)
Balance at end of period, common equity		$ (7)	$ (3)

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

[2] 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).

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