Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended					9 Months Ended
		Sep. 30, 2021		Jun. 30, 2021	Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020		Dec. 31, 2020		Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Unfunded commitments, equity securities measured at net asset value		$ 29					$ 29				$ 33
Revaluation period							90 days
Deferred fees		5					$ 5				3
Derivative financial assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		319			$ 343		319		$ 343
Derivative financial liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities		247			239		247		239
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		207		$ 130	252		207		252		319		$ 758	$ 707
Fair value of level 3 liabilities		1,999		1,512	1,022		1,999		1,022		1,094		1,019	1,128
Assets, Transfers Into Level 3		(38)			20		(30)		28
Assets, Transfers Out of Level 3		0			(1)		(52)		1
Fair Value Liability, Transfers Into Level 3		9			1		154		1
Transfers Out of Level 3		27			11		115		75
Level 3 [Member] | Equity contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivatives, net, Transfers out of Level 3		0	[1]	(27)	(1)	[1]	(28)	[1]	1	[1]
Derivatives, net, Transfers into Level 3	[1]	38			0		30		0
Unfunded Loan Commitment [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees		140					140				137
Deposits [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities		516	[2],[3],[4]	593	650	[2]	516	[2],[3],[4]	650	[2]	646	[2],[3],[4]	672	774	[2]
Fair Value Liability, Transfers Into Level 3		0			0		109	[2]	0	[2]
Transfers Out of Level 3		9			8		90	[2]	56	[2]
Long-term debt [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities		1,483	[2],[3],[4]	919	372	[2]	1,483	[2],[3],[4]	372	[2]	448	[2],[3],[4]	347	354	[2]
Fair Value Liability, Transfers Into Level 3		9			1		45	[2]	1	[2]
Transfers Out of Level 3		18			3		25	[2]	19	[2]
Asset-backed Securities Available-for-sale [Member] | Level 3 [Member] | Available-for-sale securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		121	[5]	126	127	[5]	121	[5]	127	[5]	131	[5]	117	111	[5]
Assets, Transfers Into Level 3		0			20		0	[5]	28	[5]
Assets, Transfers Out of Level 3		0			0		0	[5]	0	[5]
Asset-backed securities collateralized by residential mortgages [Member] | Level 3 [Member] | Trading assets, excluding derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets	[6]	$ 0			15		0		15		$ 15		$ 15	$ 17
Assets, Transfers Into Level 3	[6]				0		0		0
Assets, Transfers Out of Level 3				$ (24)	$ 0	[6]	$ (24)	[6]	$ 0	[6]

[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] 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).

[3] 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.

[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] 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).

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