Fair Value Measurements - Additional Information (Detail) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees		$ 2		$ 2			$ 1
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount		0	$ 0	$ 0	$ 0
Revaluation period				90 days
Unfunded commitments, equity securities measured at net asset value		39		$ 39			43
Derivative financial assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		156	294	156	294
Derivative financial liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	128	169	128	169
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		2,160	2,178	2,160	2,178	$ 2,113	2,207	$ 2,172	$ 3,356
Fair value of level 3 liabilities		1,475	1,498	1,475	1,498	1,433	1,538	1,683	1,906
Fair Value Assets, Transfers Into Level 3		108	0	107	0
Fair Value Assets, Transfers Out of Level 3		(1)	(2)	1	1
Fair Value Liability, Transfers Into Level 3		7	4	20	27
Fair Value Liability, Transfers Out of Level 3		73	109	275	261
Level 3 [Member] | Foreign exchange contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets	[2]	(1)	0	(1)	0	(1)	0	0	0
Fair Value Assets, Transfers Into Level 3	[2]	0	0	0	0
Fair Value Assets, Transfers Out of Level 3	[2]	0	0	0	0
Level 3 [Member] | Equity contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets	[2]	10	56	10	56	2	81	32	(2)
Fair Value Assets, Transfers Into Level 3	[2]	0	0	(1)	0
Fair Value Assets, Transfers Out of Level 3	[2]	(1)	(2)	1	1
Domestic Deposits [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	943	945	943	945	876	897	1,142	1,407
Fair Value Liability, Transfers Into Level 3	[1]	7	4	20	25
Fair Value Liability, Transfers Out of Level 3	[1]	30	82	157	184
Borrowings [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	532	553	532	553	557	641	$ 541	$ 499
Fair Value Liability, Transfers Into Level 3	[1]	0	0	0	2
Fair Value Liability, Transfers Out of Level 3	[1]	43	$ 27	118	$ 77
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		16		16		0	0
Fair Value Assets, Transfers Into Level 3		16		16
Fair Value Assets, Transfers Out of Level 3		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		92		92		$ 0	0
Fair Value Assets, Transfers Into Level 3		92		92
Fair Value Assets, Transfers Out of Level 3		0		0
Unfunded Loan Commitment [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees		166		166			$ 158
Fair Value, Measurements, Recurring [Member] | 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		16		16
Fair Value, Measurements, Recurring [Member] | 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		$ 92		$ 92
Measurement Input, Implied Volatility of Currency Pairs [Member] | Fair Value, Measurements, Recurring [Member] | Valuation Technique, Option Pricing Model [Member] | Foreign exchange contracts [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[3]	0.08		0.08			0.06
Measurement Input, Implied Volatility of Currency Pairs [Member] | Fair Value, Measurements, Recurring [Member] | Valuation Technique, Option Pricing Model [Member] | Foreign exchange contracts [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[3]	0.10		0.10			0.09
Measurement Input, Implied Volatility of Currency Pairs [Member] | Fair Value, Measurements, Recurring [Member] | Valuation Technique, Option Pricing Model [Member] | Foreign exchange contracts [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[3]	0.03		0.03
Measurement Input, Loss Severity Rates [Member] | Residential Mortgage [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Loans Held-for-sale, Measurement Input		0.70		0.70
Measurement Input, Loss Severity Rates [Member] | Impaired commercial loans [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Loans Held-for-sale, Measurement Input		0.41		0.41
Measurement Input, Equity / Equity Index Volatility [Member] | Fair Value, Measurements, Recurring [Member] | Valuation Technique, Option Pricing Model [Member] | Equity contracts [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[3]	0.07		0.07			0.07
Measurement Input, Equity / Equity Index Volatility [Member] | Fair Value, Measurements, Recurring [Member] | Valuation Technique, Option Pricing Model [Member] | Equity contracts [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[3]	0.37		0.37			0.42
Measurement Input, Equity / Equity Index Volatility [Member] | Fair Value, Measurements, Recurring [Member] | Valuation Technique, Option Pricing Model [Member] | Equity contracts [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[3]	0.07		0.07

[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 on instruments designated at fair value and related derivatives in the consolidated statement of income.

[2] Level 3 net derivatives included derivative assets of $156 million and derivative liabilities of $128 million at September 30, 2018 and derivative assets of $294 million and derivative liabilities of $169 million at September 30, 2017. Gains (losses) on derivatives, net are predominantly included in trading revenue in the consolidated statement of income.

[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.