Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Unfunded commitments, equity securities measured at net asset value		$ 33		$ 41
Revaluation period		90 days
Deferred fees		$ 3		2
Derivative financial assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		692		287
Derivative financial liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	526		222
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		312		703		$ 2,088
Fair value of level 3 liabilities		1,094		1,128		1,337
Fair Value Assets, Transfers Into Level 3		3		(17)
Fair Value Assets, Transfers Out of Level 3		2		(152)
Fair Value Liability, Transfers Into Level 3		1		7
Fair Value Liability, Transfers Out of Level 3		85		341
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]	2		1
Derivatives, net, Transfers into Level 3	[2]	37		0
Unfunded Loan Commitment [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees		137		162
Deposits [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	646	[3],[4]	774	[3],[4]	925
Fair Value Liability, Transfers Into Level 3	[1]	0		7
Fair Value Liability, Transfers Out of Level 3	[1]	63		223
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]	448	[3],[4]	354	[3],[4]	412
Fair Value Liability, Transfers Into Level 3	[1]	1		0
Fair Value Liability, Transfers Out of Level 3	[1]	22		118
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]			0		100
Fair Value Assets, Transfers Into Level 3	[5]			0
Fair Value Assets, Transfers Out of Level 3	[5]			(72)
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]			0		92
Fair Value Assets, Transfers Into Level 3	[5]			0
Fair Value Assets, Transfers Out of Level 3	[5]			(80)
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	[6]	131		111		$ 107
Fair Value Assets, Transfers Into Level 3	[6]	28		0
Fair Value Assets, Transfers Out of Level 3	[6]	$ 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 $692 million and derivative liabilities of $526 million at December 31, 2020 and derivative assets of $287 million and derivative liabilities of $222 million at December 31, 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).

[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.