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, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Assets, Beginning Balance		$ 754		$ 898		$ 703		$ 2,088
Fair Value Assets, Gains (Losses) Included In Earnings		29		19		77		101
Fair Value Assets, Gains (Losses) Included in Other Comprehensive Income		(8)		2		(10)		8
Fair Value Assets, Purchases		0		0		0		0
Fair Value Assets, Issuances		0		0		0		0
Fair Value Assets, Settlements		(548)		(6)		(553)		(1,278)
Fair Value Assets, Transfers Into Level 3		20		(21)		28		(21)
Fair Value Assets, Transfers Out of Level 3		(1)		4		1		(2)
Fair Value Assets, Ending Balance		246		896		246		896
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Earnings		29		17		92		126	[1]
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income , Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	[1]	(8)		2		(10)		8
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Liability, Beginning Balance		(1,019)		(1,371)		(1,128)		(1,337)
Fair Value Liability, Gains (Losses) Included In Earnings		(31)		(11)		20		(118)
Fair Value, Liability, Gains (Losses) Included in Other Comprehensive Income		(3)		(7)		1		(12)
Fair Value Liability, Purchases		0		0		0		0
Fair Value Liability, Issuances		(24)		(57)		(205)		(266)
Fair Value Liability, Settlements		45		130		216		272
Fair Value Liability, Transfers Into Level 3		(1)		(1)		(1)		(6)
Fair Value Liability, Transfers Out of Level 3		11		128		75		278
Fair Value Liability, Ending Balance		(1,022)		(1,189)		(1,022)		(1,189)
Fair Value Liability, Current Period Unrealized Gains (Losses) Included in Earnings		(25)		0		4		(191)	[2]
Fair Value Liability, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income	[2]	(3)		(7)		1		(12)
Interest rate contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Derivatives, net, Beginning Balance	[3]	33		10		10		2
Derivatives, net, Gains (Losses) included in Earnings	[3]	1		18		24		31
Derivatives, net, Gains (Losses) included in Other Comprehensive Income	[3]	0		0		0		0
Derivatives, net, Purchases	[3]	0		0		0		0
Derivatives, net, Issuances	[3]	0		0		0		0
Derivatives, net, Settlements	[3]	0		0		0		0
Derivatives, net, Transfers into Level 3	[3]	0		0		0		0
Derivatives, net, Transfers out of Level 3	[3]	0		0		0		(5)
Derivatives, net, Ending Balance	[3]	34		28		34		28
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Earnings	[3]	1		17		24		25
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income	[3]	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	[3]	(2)		(1)		(1)	[4]	(1)
Derivatives, net, Gains (Losses) included in Earnings	[3]	0		4		(1)		4
Derivatives, net, Gains (Losses) included in Other Comprehensive Income	[3]	0		0		0		0
Derivatives, net, Purchases	[3]	0		0		0		0
Derivatives, net, Issuances	[3]	0		0		0		0
Derivatives, net, Settlements	[3]	0		0		0		0
Derivatives, net, Transfers into Level 3	[3]	0		(21)		0		(21)
Derivatives, net, Transfers out of Level 3	[3]	0		0		0		0
Derivatives, net, Ending Balance	[3]	(2)	[4]	(18)		(2)	[4]	(18)
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Earnings	[3]	0		3		(1)		3
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income	[3]	0		0		0		0
Equity contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Derivatives, net, Beginning Balance	[3]	92		62		72	[4]	(52)
Derivatives, net, Gains (Losses) included in Earnings	[3]	50		3		62		113
Derivatives, net, Gains (Losses) included in Other Comprehensive Income	[3]	0		0		0		0
Derivatives, net, Purchases	[3]	0		0		0		0
Derivatives, net, Issuances	[3]	0		0		0		0
Derivatives, net, Settlements	[3]	(75)		(2)		(69)		3
Derivatives, net, Transfers into Level 3	[3]	0		0		0		0
Derivatives, net, Transfers out of Level 3	[3]	(1)		4		1		3
Derivatives, net, Ending Balance	[3]	66	[4]	67		66	[4]	67
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Earnings	[3]	44		0		76		115
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income	[3]	0		0		0		0
Credit contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Derivatives, net, Beginning Balance	[3]	62		46		59		52
Derivatives, net, Gains (Losses) included in Earnings	[3]	(16)		(2)		10		(42)
Derivatives, net, Gains (Losses) included in Other Comprehensive Income	[3]	0		0		0		0
Derivatives, net, Purchases	[3]	0		0		0		0
Derivatives, net, Issuances	[3]	0		0		0		0
Derivatives, net, Settlements	[3]	19		(4)		(4)		30
Derivatives, net, Transfers into Level 3	[3]	0		0		0		0
Derivatives, net, Transfers out of Level 3	[3]	0		0		0		0
Derivatives, net, Ending Balance	[3]	65		40		65		40
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Earnings	[3]	(16)		(2)		(5)		(4)
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income	[3]	0		0		0		0
Other Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Derivatives, net, Beginning Balance	[3]	(64)		(35)		(75)		(35)
Derivatives, net, Gains (Losses) included in Earnings	[3]	(2)		(4)		(3)		(13)
Derivatives, net, Gains (Losses) included in Other Comprehensive Income	[3]	0		0		0		0
Derivatives, net, Purchases	[3]	0		0		0		0
Derivatives, net, Issuances	[3]	0		0		0		0
Derivatives, net, Settlements	[3]	7		6		19		15
Derivatives, net, Transfers into Level 3	[3]	0		0		0		0
Derivatives, net, Transfers out of Level 3	[3]	0		0		0		0
Derivatives, net, Ending Balance	[3]	(59)		(33)		(59)		(33)
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Earnings	[3]	0		0		0		0
Derivatives, net, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income	[3]	0		0		0		0
Other assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Assets, Beginning Balance	[5]			1				4
Fair Value Assets, Gains (Losses) Included In Earnings	[5]			0				0
Fair Value Assets, Gains (Losses) Included in Other Comprehensive Income	[5]			0				0
Fair Value Assets, Purchases	[5]			0				0
Fair Value Assets, Issuances	[5]			0				0
Fair Value Assets, Settlements	[5]			(1)				(4)
Fair Value Assets, Transfers Into Level 3	[5]			0				0
Fair Value Assets, Transfers Out of Level 3	[5]			0				0
Fair Value Assets, Ending Balance	[5]			0				0
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Earnings				0	[5]			0	[1]
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income , Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	[1]			0				0
Collateralized debt obligations [Member] | Trading assets, excluding derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Assets, Beginning Balance	[1]			86				100
Fair Value Assets, Gains (Losses) Included In Earnings	[1]			(1)				2
Fair Value Assets, Gains (Losses) Included in Other Comprehensive Income	[1]			0				0
Fair Value Assets, Purchases	[1]			0				0
Fair Value Assets, Issuances	[1]			0				0
Fair Value Assets, Settlements	[1]			(1)				(18)
Fair Value Assets, Transfers Into Level 3	[1]			0				0
Fair Value Assets, Transfers Out of Level 3	[1]			0				0
Fair Value Assets, Ending Balance	[1]			84				84
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Earnings	[1]			(1)				(11)
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income , Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	[1]			0				0
Residential mortgage asset-backed securities [Member] | Trading assets, excluding derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Assets, Beginning Balance	[1]	15		16		17		16
Fair Value Assets, Gains (Losses) Included In Earnings	[1]	0		1		(2)		1
Fair Value Assets, Gains (Losses) Included in Other Comprehensive Income	[1]	0		0		0		0
Fair Value Assets, Purchases	[1]	0		0		0		0
Fair Value Assets, Issuances	[1]	0		0		0		0
Fair Value Assets, Settlements	[1]	0		0		0		0
Fair Value Assets, Transfers Into Level 3		0	[1]	0	[1]	0		0	[1]
Fair Value Assets, Transfers Out of Level 3	[1]	0		0		0		0
Fair Value Assets, Ending Balance	[1]	15		17		15		17
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Earnings	[1]	0		0		(2)		0
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income , Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	[1]	0		0		0		0
Student loan asset-backed securities [Member] | Trading assets, excluding derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Assets, Beginning Balance	[1]			90				92
Fair Value Assets, Gains (Losses) Included In Earnings	[1]			0				5
Fair Value Assets, Gains (Losses) Included in Other Comprehensive Income	[1]			0				0
Fair Value Assets, Purchases	[1]			0				0
Fair Value Assets, Issuances	[1]			0				0
Fair Value Assets, Settlements	[1]			(4)				(11)
Fair Value Assets, Transfers Into Level 3	[1]			0				0
Fair Value Assets, Transfers Out of Level 3	[1]			0				0
Fair Value Assets, Ending Balance	[1]			86				86
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Earnings	[1]			0				(2)
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income , Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	[1]			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]
Fair Value Assets, Beginning Balance	[1]	501		510		510		1,803
Fair Value Assets, Gains (Losses) Included In Earnings	[1]	(4)		0		(13)		0
Fair Value Assets, Gains (Losses) Included in Other Comprehensive Income	[1]	0		0		0		0
Fair Value Assets, Purchases	[1]	0		0		0		0
Fair Value Assets, Issuances	[1]	0		0		0		0
Fair Value Assets, Settlements	[1]	(497)		0		(497)		(1,293)
Fair Value Assets, Transfers Into Level 3	[1]	0		0		0		0
Fair Value Assets, Transfers Out of Level 3	[1]	0		0		0		0
Fair Value Assets, Ending Balance	[1]	0		510		0		510
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Earnings	[1]	0		0		0		0
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income , Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	[1]	0		0		0		0
Other | Available-for-sale securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Assets, Beginning Balance	[6]	117		113		111		107
Fair Value Assets, Gains (Losses) Included In Earnings	[6]	0		0		0		0
Fair Value Assets, Gains (Losses) Included in Other Comprehensive Income		(8)	[6]	2	[3]	(10)	[6]	8	[6]
Fair Value Assets, Purchases	[6]	0		0		0		0
Fair Value Assets, Issuances	[6]	0		0		0		0
Fair Value Assets, Settlements	[6]	(2)		0		(2)		0
Fair Value Assets, Transfers Into Level 3	[6]	20		0		28		0
Fair Value Assets, Transfers Out of Level 3	[6]	0		0		0		0
Fair Value Assets, Ending Balance	[6]	127		115		127		115
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Earnings		0	[6]	0	[6]	0	[6]	0	[1]
Fair Value Assets, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income , Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	[1]	(8)		2		(10)		8
Domestic Deposits [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Liability, Beginning Balance	[2]	(672)		(930)		(774)	[4],[7]	(925)
Fair Value Liability, Gains (Losses) Included In Earnings	[2]	(10)		(27)		3		(91)
Fair Value, Liability, Gains (Losses) Included in Other Comprehensive Income	[2]	(3)		(5)		(1)		(8)
Fair Value Liability, Purchases	[2]	0		0		0		0
Fair Value Liability, Issuances	[2]	0		(30)		(43)		(175)
Fair Value Liability, Settlements	[2]	27		57		109		166
Fair Value Liability, Transfers Into Level 3	[2]	0		(1)		0		(6)
Fair Value Liability, Transfers Out of Level 3	[2]	8		83		56		186
Fair Value Liability, Ending Balance	[2]	(650)	[4],[7]	(853)		(650)	[4],[7]	(853)
Fair Value Liability, Current Period Unrealized Gains (Losses) Included in Earnings	[2]	(8)		(24)		(1)		(156)
Fair Value Liability, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income	[2]	(3)		(5)		(1)		(8)
Long-term debt [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Liability, Beginning Balance	[2]	(347)		(441)		(354)	[4],[7]	(412)
Fair Value Liability, Gains (Losses) Included In Earnings	[2]	(21)		16		17		(27)
Fair Value, Liability, Gains (Losses) Included in Other Comprehensive Income	[2]	0		(2)		2		(4)
Fair Value Liability, Purchases	[2]	0		0		0		0
Fair Value Liability, Issuances	[2]	(24)		(27)		(162)		(91)
Fair Value Liability, Settlements	[2]	18		73		107		106
Fair Value Liability, Transfers Into Level 3	[2]	(1)		0		(1)		0
Fair Value Liability, Transfers Out of Level 3	[2]	3		45		19		92
Fair Value Liability, Ending Balance	[2]	(372)	[4],[7]	(336)		(372)	[4],[7]	(336)
Fair Value Liability, Current Period Unrealized Gains (Losses) Included in Earnings	[2]	(17)		24		5		(35)
Fair Value Liability, Current Period Unrealized Gains (Losses) Included in Other Comprehensive Income	[2]	$ 0		$ (2)		$ 2		$ (4)

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

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

[3] Level 3 net derivatives included derivative assets of $343 million and derivative liabilities of $239 million at September 30, 2020 and derivative assets of $436 million and derivative liabilities of $352 million at September 30, 2019. Gains (losses) on derivatives, net are predominantly included in trading revenue and gain (loss) on instruments designated at fair value and related derivatives in the consolidated statement of income (loss).

[4] 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.

[5] Represented contingent consideration receivable associated with the sale of certain private banking client relationships, which concluded in 2019. Gains (losses) associated with this transaction were included in other income (loss) 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.

[7] 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.