Fair Value Measurements - Additional Information (Detail) $ in Millions		3 Months Ended
		Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees		$ 2		$ 2
Revaluation period		90 days
Unfunded commitments, equity securities measured at net asset value		$ 79		72
Derivative financial assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		288	$ 281
Derivative financial liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	242	185
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 assets		870	2,152	2,088	$ 2,207
Fair value of level 3 liabilities		1,402	1,546	1,337	1,538
Fair Value Assets, Transfers Into Level 3		0	0
Fair Value Assets, Transfers Out of Level 3		1	0
Fair Value Liability, Transfers Into Level 3		0	3
Fair Value Liability, Transfers Out of Level 3		69	78
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
Fair Value Assets, Transfers Into Level 3	[2]	0	0
Fair Value Assets, Transfers Out of Level 3	[2]	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]	24	27	(52)	81
Fair Value Assets, Transfers Into Level 3	[2]	0	0
Fair Value Assets, Transfers Out of Level 3	[2]	1	0
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	[3]	90	131	100	129
Fair Value Assets, Transfers Into Level 3	[3]	0	0
Fair Value Assets, Transfers Out of Level 3	[3]	0	0
Domestic Deposits [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	949	916	925	897
Fair Value Liability, Transfers Into Level 3	[1]	0	3
Fair Value Liability, Transfers Out of Level 3	[1]	61	34
Borrowings [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of level 3 liabilities	[1]	453	630	412	$ 641
Fair Value Liability, Transfers Into Level 3	[1]	0	0
Fair Value Liability, Transfers Out of Level 3	[1]	8	$ 44
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	[3]	16		16
Fair Value Assets, Transfers Into Level 3		0
Fair Value Assets, Transfers Out of Level 3	[3]	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		95		92
Fair Value Assets, Transfers Into Level 3		0
Fair Value Assets, Transfers Out of Level 3		0
Unfunded Loan Commitment [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Deferred fees		$ 160		$ 165
Measurement Input, Prepayment Rates [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized debt obligations [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.00		0.00
Measurement Input, Prepayment Rates [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized debt obligations [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.01		0.01
Measurement Input, Prepayment Rates [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized debt obligations [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.004
Measurement Input, Prepayment Rates [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.00		0.00
Measurement Input, Prepayment Rates [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.05		0.05
Measurement Input, Prepayment Rates [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.05
Measurement Input, Prepayment Rates [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.07		0.06
Measurement Input, Prepayment Rates [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.08		0.07
Measurement Input, Prepayment Rates [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.08
Measurement Input, Default Rate [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized debt obligations [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.00		0.00
Measurement Input, Default Rate [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized debt obligations [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.01		0.01
Measurement Input, Default Rate [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized debt obligations [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.009
Measurement Input, Default Rate [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.01		0.01
Measurement Input, Default Rate [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.03		0.04
Measurement Input, Default Rate [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.03
Measurement Input, Default Rate [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.00		0.01
Measurement Input, Default Rate [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.01		0.02
Measurement Input, Default Rate [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.008
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	[4]	0.12		0.08
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	[4]	0.17		0.12
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	[4]	0.09
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		0.32
Measurement Input, Loss Severity Rates [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized debt obligations [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.90		0.90
Measurement Input, Loss Severity Rates [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized debt obligations [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.95		0.95
Measurement Input, Loss Severity Rates [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized debt obligations [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.93
Measurement Input, Loss Severity Rates [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.80		0.80
Measurement Input, Loss Severity Rates [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.85		0.85
Measurement Input, Loss Severity Rates [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.85
Measurement Input, Loss Severity Rates [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.25		0.25
Measurement Input, Loss Severity Rates [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.40		0.40
Measurement Input, Loss Severity Rates [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.36
Measurement Input, Discount Margin [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.0100		0.0100
Measurement Input, Discount Margin [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.0250		0.0250
Measurement Input, Discount Margin [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.0200
Measurement Input, Discount Margin [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.0091		0.0091
Measurement Input, Discount Margin [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.0115		0.0115
Measurement Input, Discount Margin [Member] | Fair Value, Measurements, Recurring [Member] | Student loan asset-backed securities [Member] | Valuation Technique, Consensus Pricing Model [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt Securities, Trading, Measurement Input		0.0100
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	[4]	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	[4]	0.38		0.44
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	[4]	0.12

[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] Level 3 net derivatives included derivative assets of $288 million and derivative liabilities of $242 million at March 31, 2019 and derivative assets of $281 million and derivative liabilities of $185 million at March 31, 2018. 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] Gains (losses) on trading assets, excluding derivatives are included in trading revenue in the consolidated statement of income (loss).

[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.