Fair Value Measurements - Changes in Fair Value of Level 3 Assets and Liabilities (Detail) - Level 3 [Member] - USD ($) $ in Millions		3 Months Ended					9 Months Ended
		Sep. 30, 2021		Jun. 30, 2021	Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total assets, beginning balance		$ 130			$ 758		$ 319		$ 707
Assets, Total Realized/Unrealized Gains (Losses) Included in Earnings		(144)			29		(330)		75
Assets, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income		(2)			(8)		(3)		(10)
Assets, Purchases		0			0		0		0
Assets, Issuances		1			2		7		4
Assets, Settlements		260			(548)		296		(553)
Assets, Transfers Into Level 3		(38)			20		(30)		28
Assets, Transfers Out of Level 3		0			(1)		(52)		1
Total assets, ending balance		207		$ 130	252		207		252
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Earnings		(1)			29		4		90
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income		(2)			(8)		(3)		(10)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total liabilities, beginning balance		(1,512)			(1,019)		(1,094)		(1,128)
Total Realized/Unrealized Gains (Losses) Included in Earnings		42			(31)		11		20
Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income		1			(3)		1		1
Purchases		0			0		0		0
Issuances		(660)			(24)		(1,201)		(205)
Settlements		112			45		323		216
Transfers Into Level 3		(9)			(1)		(154)		(1)
Transfers Out of Level 3		27			11		115		75
Total liabilities, ending balance		(1,999)		(1,512)	(1,022)		(1,999)		(1,022)
Current Period Unrealized Gains (Losses) Still Held Included in Earnings		40			(25)		17		4
Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income		1			(3)		1		1
Interest rate contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Derivatives, net, Beginning Balance	[1]	8			33		34		10
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Earnings	[1]	(8)			1		(34)		24
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income	[1]	0			0		0		0
Derivatives, net, Purchases	[1]	0			0		0		0
Derivatives, net, Issuances	[1]	0			0		0		0
Derivatives, net, Settlements	[1]	0			0		0		0
Derivatives, net, Transfers into Level 3	[1]	0			0		0		0
Derivatives, net, Transfers out of Level 3	[1]	0			0		0		0
Derivatives, net, Ending Balance	[1]	0		8	34		0		34
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Earnings	[1]	0			1		(5)		24
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income	[1]	0			0		0		0
Foreign exchange contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Derivatives, net, Beginning Balance	[1]	(1)			(2)		9	[2]	(1)
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Earnings	[1]	0			0		(10)		(1)
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income	[1]	0			0		0		0
Derivatives, net, Purchases	[1]	0			0		0		0
Derivatives, net, Issuances	[1]	0			0		0		0
Derivatives, net, Settlements	[1]	0			0		0		0
Derivatives, net, Transfers into Level 3	[1]	0			0		0		0
Derivatives, net, Transfers out of Level 3	[1]	0			0		0		0
Derivatives, net, Ending Balance	[1]	(1)	[2]	(1)	(2)		(1)	[2]	(2)
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Earnings	[1]	0			0		(11)		(1)
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income	[1]	0			0		0		0
Equity contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Derivatives, net, Beginning Balance	[1]	(13)			92		119	[2]	72
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Earnings	[1]	(91)			50		(230)		62
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income	[1]	0			0		0		0
Derivatives, net, Purchases	[1]	0			0		0		0
Derivatives, net, Issuances	[1]	0			0		0		0
Derivatives, net, Settlements	[1]	256			(75)		283		(69)
Derivatives, net, Transfers into Level 3	[1]	(38)			0		(30)		0
Derivatives, net, Transfers out of Level 3		0	[1]	(27)	(1)	[1]	(28)	[1]	1	[1]
Derivatives, net, Ending Balance	[1]	114	[2]	(13)	66		114	[2]	66
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Earnings	[1]	(2)			44		22		76
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income	[1]	0			0		0		0
Credit contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Derivatives, net, Beginning Balance	[1]	46			62		63		59
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Earnings	[1]	(49)			(16)		(65)		10
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income	[1]	0			0		0		0
Derivatives, net, Purchases	[1]	0			0		0		0
Derivatives, net, Issuances	[1]	0			0		0		0
Derivatives, net, Settlements	[1]	1			19		0		(4)
Derivatives, net, Transfers into Level 3	[1]	0			0		0		0
Derivatives, net, Transfers out of Level 3	[1]	0			0		0		0
Derivatives, net, Ending Balance	[1]	(2)		46	65		(2)		65
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Earnings	[1]	0			(16)		(2)		(5)
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income	[1]	0			0		0		0
Other Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Derivatives, net, Beginning Balance	[1]	(48)			(64)		(59)		(75)	[3]
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Earnings	[1]	3			(2)		0		(3)	[3]
Derivatives, net, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income	[1]	0			0		0		0	[3]
Derivatives, net, Purchases	[1]	0			0		0		0	[3]
Derivatives, net, Issuances	[1]	0			0		0		0	[3]
Derivatives, net, Settlements	[1]	6			7		20		19	[3]
Derivatives, net, Transfers into Level 3	[1]	0			0		0		0	[3]
Derivatives, net, Transfers out of Level 3	[1]	0			0		0		0	[3]
Derivatives, net, Ending Balance	[1]	(39)		(48)	(59)	[3]	(39)		(59)	[3]
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Earnings	[1]	0			0		0		0	[3]
Derivatives, net, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income	[1]	0			0		0		0	[3]
Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total assets, beginning balance		12			4		7	[4]	4	[4]
Assets, Total Realized/Unrealized Gains (Losses) Included in Earnings		1			0		0	[4]	(2)	[4]
Assets, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income		0			0		0	[4]	0	[4]
Assets, Purchases		0			0		0	[4]	0	[4]
Assets, Issuances		1			2		7	[4]	4	[4]
Assets, Settlements		0			0		0	[4]	0	[4]
Assets, Transfers Into Level 3		0			0		0	[4]	0	[4]
Assets, Transfers Out of Level 3		0			0		0	[4]	0	[4]
Total assets, ending balance		14	[4]	12	6	[4]	14	[4]	6	[4]
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Earnings		1			0		0	[4]	(2)	[4]
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income		0			0		0	[4]	0	[4]
Residential mortgage asset-backed securities [Member] | Trading assets, excluding derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total assets, beginning balance	[5]				15		15		17
Assets, Total Realized/Unrealized Gains (Losses) Included in Earnings	[5]				0		9		(2)
Assets, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income	[5]				0		0		0
Assets, Purchases	[5]				0		0		0
Assets, Issuances	[5]				0		0		0
Assets, Settlements	[5]				0		0		0
Assets, Transfers Into Level 3	[5]				0		0		0
Assets, Transfers Out of Level 3				(24)	0	[5]	(24)	[5]	0	[5]
Total assets, ending balance	[5]	0			15		0		15
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Earnings	[5]				0		0		(2)
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income	[5]				0		0		0
Corporate and other domestic debt securities [Member] | Trading assets, excluding derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total assets, beginning balance	[5]				501				510
Assets, Total Realized/Unrealized Gains (Losses) Included in Earnings	[5]				(4)				(13)
Assets, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income	[5]				0				0
Assets, Purchases	[5]				0				0
Assets, Issuances	[5]				0				0
Assets, Settlements	[5]				(497)				(497)
Assets, Transfers Into Level 3	[5]				0				0
Assets, Transfers Out of Level 3	[5]				0				0
Total assets, ending balance	[5]				0				0
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Earnings	[5]				0				0
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income	[5]				0				0
Other [Member] | Available-for-sale securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total assets, beginning balance		126			117		131	[6]	111	[6]
Assets, Total Realized/Unrealized Gains (Losses) Included in Earnings		0			0		0	[6]	0	[6]
Assets, Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income		(2)			(8)	[1]	(3)	[6]	(10)	[6]
Assets, Purchases		0			0		0	[6]	0	[6]
Assets, Issuances		0			0		0	[6]	0	[6]
Assets, Settlements		(3)			(2)		(7)	[6]	(2)	[6]
Assets, Transfers Into Level 3		0			20		0	[6]	28	[6]
Assets, Transfers Out of Level 3		0			0		0	[6]	0	[6]
Total assets, ending balance		121	[6]	126	127	[6]	121	[6]	127	[6]
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Earnings		0			0		0	[6]	0	[6]
Assets, Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income		(2)			(8)		(3)	[6]	(10)	[6]
Domestic Deposits [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total liabilities, beginning balance		(593)			(672)		(646)	[2],[7],[8]	(774)	[7]
Total Realized/Unrealized Gains (Losses) Included in Earnings		9			(10)		1	[7]	3	[7]
Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income		1			(3)		2	[7]	(1)	[7]
Purchases		0			0		0	[7]	0	[7]
Issuances		0			0		0	[7]	(43)	[7]
Settlements		58			27		146	[7]	109	[7]
Transfers Into Level 3		0			0		(109)	[7]	0	[7]
Transfers Out of Level 3		9			8		90	[7]	56	[7]
Total liabilities, ending balance		(516)	[2],[7],[8]	(593)	(650)	[7]	(516)	[2],[7],[8]	(650)	[7]
Current Period Unrealized Gains (Losses) Still Held Included in Earnings		6			(8)		3	[7]	(1)	[7]
Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income		1			(3)		2	[7]	(1)	[7]
Long-term debt [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total liabilities, beginning balance		(919)			(347)		(448)	[2],[7],[8]	(354)	[7]
Total Realized/Unrealized Gains (Losses) Included in Earnings		33			(21)		10	[7]	17	[7]
Total Realized/Unrealized Gains (Losses) Included in Other Comprehensive Income		0			0		(1)	[7]	2	[7]
Purchases		0			0		0	[7]	0	[7]
Issuances		(660)			(24)		(1,201)	[7]	(162)	[7]
Settlements		54			18		177	[7]	107	[7]
Transfers Into Level 3		(9)			(1)		(45)	[7]	(1)	[7]
Transfers Out of Level 3		18			3		25	[7]	19	[7]
Total liabilities, ending balance		(1,483)	[2],[7],[8]	$ (919)	(372)	[7]	(1,483)	[2],[7],[8]	(372)	[7]
Current Period Unrealized Gains (Losses) Still Held Included in Earnings		34			(17)		14	[7]	5	[7]
Current Period Unrealized Gains (Losses) Still Held Included in Other Comprehensive Income		$ 0			$ 0		$ (1)	[7]	$ 2	[7]

[1] Level 3 net derivatives included derivative assets of $319 million and derivative liabilities of $247 million at September 30, 2021 and derivative assets of $343 million and derivative liabilities of $239 million at September 30, 2020. Gains (losses) on derivatives, net are predominantly included in trading revenue (expense) and gain on instruments designated at fair value and related derivatives in the consolidated statement of income (loss).

[2] We are the client-facing entity and we enter into identical but opposite derivatives to transfer the resultant risks to our affiliates. With the exception of counterparty credit risks, we are market neutral. The corresponding intra-group derivatives are presented as equity derivatives and foreign exchange derivatives in the table.

[3] Consists of swap agreements entered into in conjunction with the sales of Visa Class B Shares. Gains (losses) on these swap agreements are included in other income (loss) in the consolidated statement of income (loss).

[4] Gain (losses) on mortgage servicing rights are included in other income (loss) in the consolidated statement of income (loss).

[5] Gains (losses) on trading assets, excluding derivatives are included in trading revenue (expense) in the consolidated statement of income (loss).

[6] Realized gains (losses) on securities available-for-sale are included in other securities gains, net in the consolidated statement of income (loss). Changes in the allowance for credit losses on securities available-for-sale are included in the provision for credit losses in the consolidated statement of income (loss). Unrealized gains (losses) on securities available-for-sale are included in other comprehensive income (loss).

[7] Excluding unrealized gains (losses) on fair value option liabilities attributable to our own credit spread, which are recorded in other comprehensive income (loss), gains (losses) on fair value option liabilities are included in gain on instruments designated at fair value and related derivatives in the consolidated statement of income (loss).

[8] Structured deposits and structured notes contain embedded derivative features whose fair value measurements contain significant Level 3 inputs. See equity and foreign exchange derivatives below for a discussion of the uncertainty of Level 3 inputs related to structured deposits and structured notes.