Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2019		Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018	Jun. 30, 2019	Dec. 31, 2018		Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Unfunded commitments, equity securities measured at net asset value		$ 47			$ 47				$ 72
Revaluation period					90 days
Deferred fees		2			$ 2				2
Derivative financial assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		436		$ 156	436		$ 156
Derivative financial liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	352		128	352		128
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		896		2,160	896		2,160	$ 898	2,088		$ 2,113	$ 2,207
Fair value of level 3 liabilities		1,189		1,475	1,189		1,475	1,371	1,337		1,433	1,538
Fair Value Assets, Transfers Into Level 3		(21)		108	(21)		107
Fair Value Assets, Transfers Out of Level 3		4		(1)	(2)		1
Fair Value Liability, Transfers Into Level 3		1		7	6		20
Fair Value Liability, Transfers Out of Level 3		128		73	278		275
Unfunded Loan Commitment [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees		163			163				165
Deposits [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	853	[2],[3]	943	853	[2],[3]	943	930	925	[2],[3]	876	897
Fair Value Liability, Transfers Into Level 3	[1]	1		7	6		20
Fair Value Liability, Transfers Out of Level 3	[1]	83		30	186		157
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]	336	[2],[3]	532	336	[2],[3]	532	441	412	[2],[3]	557	641
Fair Value Liability, Transfers Into Level 3	[1]	0		0	0		0
Fair Value Liability, Transfers Out of Level 3	[1]	45		43	92		118
Residential Mortgage 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		17	[4]	16	17	[4]	16	16	16	[4]	0	0
Fair Value Assets, Transfers Into Level 3		0		16	0		16
Fair Value Assets, Transfers Out of Level 3		0		0	0	[4]	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		86		92	86		92	$ 90	$ 92		$ 0	$ 0
Fair Value Assets, Transfers Into Level 3		0		92	0		92
Fair Value Assets, Transfers Out of Level 3		$ 0		$ 0	$ 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 (loss), 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] Structured deposits and structured notes contain embedded derivative features whose fair value measurements contain significant Level 3 inputs.

[3] 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.

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