Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021		Mar. 31, 2020	Dec. 31, 2020		Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Unfunded commitments, equity securities measured at net asset value		$ 32			$ 33
Revaluation period		90 days
Deferred fees		$ 3			3
Derivative financial assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		541		$ 628
Derivative financial liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities		504		546
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		202		683	319		$ 707
Fair value of level 3 liabilities		1,085		1,024	1,094		1,128
Assets, Transfers Into Level 3		0		0
Assets, Transfers Out of Level 3		(1)		0
Fair Value Liability, Transfers Into Level 3		2		0
Transfers Out of Level 3		16		37
Level 3 [Member] | Equity contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivatives, net, Transfers out of Level 3	[1]	(1)		0
Derivatives, net, Transfers into Level 3	[1]	0		0
Unfunded Loan Commitment [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees		139			137
Deposits [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[2]	599	[3],[4]	653	646	[3],[4]	774
Fair Value Liability, Transfers Into Level 3	[2]	0		0
Transfers Out of Level 3	[2]	15		33
Long-term debt [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[2]	486	[3],[4]	371	448	[3],[4]	354
Fair Value Liability, Transfers Into Level 3	[2]	2		0
Transfers Out of Level 3	[2]	1		4
Other securities [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	[5]	130		116	$ 131		$ 111
Assets, Transfers Into Level 3	[5]	0		0
Assets, Transfers Out of Level 3	[5]	$ 0		$ 0

[1] Level 3 net derivatives included derivative assets of $541 million and derivative liabilities of $504 million at March 31, 2021 and derivative assets of $628 million and derivative liabilities of $546 million at March 31, 2020. 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).

[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] 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.