Fair Value Measurements - Quantitative Information about Recurring Fair Value Measurement of Assets and Liabilities Classified as Level 3 (Detail) - Recurring [Member] $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		$ 85,744	$ 81,030
Liabilities, Fair Value Disclosure		(50,585)	(52,587)
Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		1,112	2,301
Liabilities, Fair Value Disclosure		(1,644)	(1,550)
Deposits [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Liabilities, Fair Value Disclosure	[1],[2]	(949)	(925)
Borrowings [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Liabilities, Fair Value Disclosure	[1],[2]	(453)	(412)
Credit contracts [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		53	52
Equity contracts [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	[2]	24	(52)
Foreign exchange contracts [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	[2]	(1)	(1)
Interest rate contracts [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		7	2
Other Contracts [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		(37)	(35)
Trading assets, excluding derivatives [Member] | Collateralized debt obligations [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		90	100
Trading assets, excluding derivatives [Member] | Collateralized debt obligations [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		90	100
Trading assets, excluding derivatives [Member] | Residential mortgage asset-backed securities [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		16	16
Trading assets, excluding derivatives [Member] | Residential mortgage asset-backed securities [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		16	16
Trading assets, excluding derivatives [Member] | Student loan asset-backed securities [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		95	92
Trading assets, excluding derivatives [Member] | Student loan asset-backed securities [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		95	92
Trading assets, excluding derivatives [Member] | Corporate and other domestic debt securities [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		510	1,803
Trading assets, excluding derivatives [Member] | Corporate and other domestic debt securities [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		510	1,803
Available-for-sale securities [Member] | Other asset-backed securities available-for-sale [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	[3]	109	107
Available-for-sale securities [Member] | Other asset-backed securities available-for-sale [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	[3]	109	107
Other assets [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	[4]	4	4
Other assets [Member] | Level 3 [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	[4]	$ 4	$ 4
Measurement Input, Prepayment Rates [Member] | Collateralized debt obligations [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.00	0.00
Measurement Input, Prepayment Rates [Member] | Collateralized debt obligations [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.01	0.01
Measurement Input, Prepayment Rates [Member] | Residential mortgage asset-backed securities [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.00	0.00
Measurement Input, Prepayment Rates [Member] | Residential mortgage asset-backed securities [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.05	0.05
Measurement Input, Prepayment Rates [Member] | Student loan asset-backed securities [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.07	0.06
Measurement Input, Prepayment Rates [Member] | Student loan asset-backed securities [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.08	0.07
Measurement Input, Default Rates [Member] | Collateralized debt obligations [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.00	0.00
Measurement Input, Default Rates [Member] | Collateralized debt obligations [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.01	0.01
Measurement Input, Default Rates [Member] | Residential mortgage asset-backed securities [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.01	0.01
Measurement Input, Default Rates [Member] | Residential mortgage asset-backed securities [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.03	0.04
Measurement Input, Default Rates [Member] | Student loan asset-backed securities [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.00	0.01
Measurement Input, Default Rates [Member] | Student loan asset-backed securities [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.01	0.02
Measurement Input, Loss Severity Rates [Member] | Collateralized debt obligations [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.90	0.90
Measurement Input, Loss Severity Rates [Member] | Collateralized debt obligations [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.95	0.95
Measurement Input, Loss Severity Rates [Member] | Residential mortgage asset-backed securities [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.80	0.80
Measurement Input, Loss Severity Rates [Member] | Residential mortgage asset-backed securities [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.85	0.85
Measurement Input, Loss Severity Rates [Member] | Student loan asset-backed securities [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.25	0.25
Measurement Input, Loss Severity Rates [Member] | Student loan asset-backed securities [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.40	0.40
Measurement Input, Discount Margin [Member] | Residential mortgage asset-backed securities [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.0100	0.0100
Measurement Input, Discount Margin [Member] | Residential mortgage asset-backed securities [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.0250	0.0250
Measurement Input, Discount Margin [Member] | Student loan asset-backed securities [Member] | Minimum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.0091	0.0091
Measurement Input, Discount Margin [Member] | Student loan asset-backed securities [Member] | Maximum [Member] | Valuation Technique, Broker Quotes or Consensus Pricing [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.0115	0.0115
Measurement Input, Spread Volatility on Collateral Assets [Member] | Corporate and other domestic debt securities [Member] | Minimum [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.02	0.02
Measurement Input, Spread Volatility on Collateral Assets [Member] | Corporate and other domestic debt securities [Member] | Maximum [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.04	0.04
Measurement Input, Correlation between Insurance Claim Shortfall and Collateral Value [Member] | Corporate and other domestic debt securities [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Trading, Measurement Input		0.80	0.80
Measurement Input, Probability to Fund for Rate Lock Commitments [Member] | Interest rate contracts [Member] | Minimum [Member] | Valuation Technique, Market Comparable Adjusted for Probability to Fund [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.15	0.03
Measurement Input, Probability to Fund for Rate Lock Commitments [Member] | Interest rate contracts [Member] | Maximum [Member] | Valuation Technique, Market Comparable Adjusted for Probability to Fund [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.99	0.99
Measurement Input, Interest Rate Transaction Execution [Member] | Interest rate contracts [Member] | Minimum [Member] | Valuation Technique, Market Comparable Adjusted for Probability to Fund [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.75	0.75
Measurement Input, Interest Rate Transaction Execution [Member] | Interest rate contracts [Member] | Maximum [Member] | Valuation Technique, Market Comparable Adjusted for Probability to Fund [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		1.00	1.00
Measurement Input, Implied Volatility of Currency Pairs [Member] | Deposits [Member] | Minimum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Domestic Deposits, Measurement Input	[1],[2]	0.12	0.08
Measurement Input, Implied Volatility of Currency Pairs [Member] | Deposits [Member] | Maximum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Domestic Deposits, Measurement Input	[1],[2]	0.17	0.12
Measurement Input, Implied Volatility of Currency Pairs [Member] | Borrowings [Member] | Minimum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Long-term Debt, Measurement Input	[1],[2]	0.12	0.08
Measurement Input, Implied Volatility of Currency Pairs [Member] | Borrowings [Member] | Maximum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Long-term Debt, Measurement Input	[1],[2]	0.17	0.12
Measurement Input, Implied Volatility of Currency Pairs [Member] | Foreign exchange contracts [Member] | Minimum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[2]	0.12	0.08
Measurement Input, Implied Volatility of Currency Pairs [Member] | Foreign exchange contracts [Member] | Maximum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[2]	0.17	0.12
Measurement Input, Equity / Equity Index Volatility [Member] | Deposits [Member] | Minimum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Domestic Deposits, Measurement Input	[1],[2]	0.07	0.07
Measurement Input, Equity / Equity Index Volatility [Member] | Deposits [Member] | Maximum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Domestic Deposits, Measurement Input	[1],[2]	0.30	0.37
Measurement Input, Equity / Equity Index Volatility [Member] | Borrowings [Member] | Minimum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Long-term Debt, Measurement Input	[1],[2]	0.07	0.07
Measurement Input, Equity / Equity Index Volatility [Member] | Borrowings [Member] | Maximum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Long-term Debt, Measurement Input	[1],[2]	0.31	0.42
Measurement Input, Equity / Equity Index Volatility [Member] | Equity contracts [Member] | Minimum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[2]	0.07	0.07
Measurement Input, Equity / Equity Index Volatility [Member] | Equity contracts [Member] | Maximum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[2]	0.38	0.44
Measurement Input, Equity/Equity and Equity/Index Correlation [Member] | Deposits [Member] | Minimum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Domestic Deposits, Measurement Input		0.44	0.42
Measurement Input, Equity/Equity and Equity/Index Correlation [Member] | Deposits [Member] | Maximum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Domestic Deposits, Measurement Input		0.48	0.49
Measurement Input, Equity/Equity and Equity/Index Correlation [Member] | Borrowings [Member] | Minimum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Long-term Debt, Measurement Input	[1],[2]	0.44	0.45
Measurement Input, Equity/Equity and Equity/Index Correlation [Member] | Borrowings [Member] | Maximum [Member] | Valuation Technique, Option Adjusted Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Long-term Debt, Measurement Input	[1],[2]	0.79	0.79
Measurement Input, Equity/Equity and Equity/Index Correlation [Member] | Equity contracts [Member] | Minimum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[2]	0.43	0.42
Measurement Input, Equity/Equity and Equity/Index Correlation [Member] | Equity contracts [Member] | Maximum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[2]	0.79	0.79
Measurement Input, Equity Dividend Yields [Member] | Equity contracts [Member] | Minimum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[2]	0.00	0.00
Measurement Input, Equity Dividend Yields [Member] | Equity contracts [Member] | Maximum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	[2]	0.05	0.07
Measurement Input, Credit Default Swap Spreads [Member] | Credit contracts [Member] | Minimum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.0069	0.0102
Measurement Input, Credit Default Swap Spreads [Member] | Credit contracts [Member] | Maximum [Member] | Valuation Technique, Option Pricing Model [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		0.0080	0.0118
Measurement Input, Conversion Rate [Member] | Other Contracts [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input		1.6	1.6
Measurement Input, Expected Duration [Member] | Other Contracts [Member] | Minimum [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Contract, Duration, Measurement Input		1 year	2 years
Measurement Input, Expected Duration [Member] | Other Contracts [Member] | Maximum [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Derivative Contract, Duration, Measurement Input		3 years	3 years
Measurement Input, Market Assumptions Related to Yields for Comparable Instruments [Member] | Other asset-backed securities available-for-sale [Member] | Minimum [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input		0.01	0.01
Measurement Input, Market Assumptions Related to Yields for Comparable Instruments [Member] | Other asset-backed securities available-for-sale [Member] | Maximum [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input		0.03	0.03
Measurement Input, Client Transfer Rates Based on Rating [Member] | Minimum [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Other Assets, Measurement Input		0.50	0.50
Measurement Input, Client Transfer Rates Based on Rating [Member] | Maximum [Member] | Valuation Technique, Discounted Cash Flows [Member]
Fair Value Measurements, Recurring, Valuation Techniques [Line Items]
Other Assets, Measurement Input		0.95	0.95

[1] Structured deposits and structured notes contain embedded derivative features whose fair value measurements contain significant Level 3 inputs.

[2] 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.

[3] Securities available-for-sale are recorded at fair value through other comprehensive income (loss).

[4] Represents contingent consideration receivable associated with the sale of a portion of our PB business.