Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019		Jun. 30, 2020	Dec. 31, 2019		Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Unfunded commitments, equity securities measured at net asset value		$ 34				$ 34					$ 41
Revaluation period						90 days
Deferred fees		3				$ 3					2
Derivative financial assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		343		$ 436		343		$ 436
Derivative financial liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	239		352		239		352
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		246		896		246		896		$ 754	703		$ 898	$ 2,088
Fair value of level 3 liabilities		1,022		1,189		1,022		1,189		1,019	1,128		1,371	1,337
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 Liability, Transfers Into Level 3		1		1		1		6
Fair Value Liability, Transfers Out of Level 3		11		128		75		278
Level 3 [Member] | Equity contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivatives, net, Transfers out of Level 3	[2]	(1)		4		1		3
Unfunded Loan Commitment [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees		142				142					162
Deposits [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	650	[3],[4]	853		650	[3],[4]	853		672	774	[3],[4]	930	925
Fair Value Liability, Transfers Into Level 3	[1]	0		1		0		6
Fair Value Liability, Transfers Out of Level 3	[1]	8		83		56		186
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]	372	[3],[4]	336		372	[3],[4]	336		347	354	[3],[4]	441	412
Fair Value Liability, Transfers Into Level 3	[1]	1		0		1		0
Fair Value Liability, Transfers Out of Level 3	[1]	3		45		19		92
Collateralized debt obligations [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	[5]			84				84					86	100
Fair Value Assets, Transfers Into Level 3	[5]			0				0
Fair Value Assets, Transfers Out of Level 3	[5]			0				0
Residential mortgage asset-backed securities [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	[5]	15		17		15		17		$ 15	$ 17		16	16
Fair Value Assets, Transfers Into Level 3		0	[5]	0	[5]	0		0	[5]
Fair Value Assets, Transfers Out of Level 3	[5]	$ 0		0		$ 0		0
Student loan asset-backed securities [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	[5]			86				86					$ 90	$ 92
Fair Value Assets, Transfers Into Level 3	[5]			0				0
Fair Value Assets, Transfers Out of Level 3	[5]			$ 0				$ 0

[1] 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).

[2] 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).

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