Fair Value Measurements - Quantitative Information about Nonrecurring Fair Value Measurement of Assets and Liabilities Classified as Level 3 (Detail) $ in Millions		Jun. 30, 2019 USD ($)		Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)		Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 898		$ 867	$ 2,088		$ 2,113	$ 2,152	$ 2,207
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		99,332			81,030
Gross Balance, Liabilities		53,059			52,587
Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1,092			2,301
Gross Balance, Liabilities		1,565			1,550
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		52			95
Fair Value, Nonrecurring [Member] | Residential mortgages [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	6
Fair Value, Nonrecurring [Member] | Impaired commercial loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[2]	30			37
Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		30			37
Fair Value, Nonrecurring [Member] | Level 3 [Member] | Residential mortgages [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	0
Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impaired commercial loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[2]	30			37
Derivative financial assets [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[3]	31,190			30,330
Derivative financial assets [Member] | Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[3]	276			179
Trading assets, excluding derivatives [Member] | Level 3 [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		16	[4]	16	16	[4]
Trading assets, excluding derivatives [Member] | Level 3 [Member] | Student loan asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		90		95	92
Trading assets, excluding derivatives [Member] | Fair Value, Recurring [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		16			16
Trading assets, excluding derivatives [Member] | Fair Value, Recurring [Member] | Student loan asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		90			92
Trading assets, excluding derivatives [Member] | Fair Value, Recurring [Member] | Level 3 [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		16			16
Trading assets, excluding derivatives [Member] | Fair Value, Recurring [Member] | Level 3 [Member] | Student loan asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		90			92
Other assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	[5]	1		$ 1	4		$ 12	$ 15	$ 15
Other assets [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]	1			4
Other assets [Member] | Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]	$ 1			$ 4
Measurement Input, Loss Severity Rates [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impaired commercial loans [Member] | Minimum [Member] | Third Party Appraisal [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Loans Held-for-sale, Measurement Input		0.00			0.13
Measurement Input, Loss Severity Rates [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member] | Impaired commercial loans [Member] | Maximum [Member] | Third Party Appraisal [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Loans Held-for-sale, Measurement Input		0.65			1.00

[1] At June 30, 2019, the fair value of the loans held for sale was below cost.

[2] Certain commercial loans have undergone troubled debt restructurings and are considered impaired. As a matter of practical expedient, we measure the credit impairment of a collateral-dependent loan based on the fair value of the collateral asset. The collateral often involves real estate properties that are illiquid due to market conditions. As a result, these loans are classified as a Level 3 fair value measurement within the fair value hierarchy.

[3] Includes trading derivative assets of $3,045 million and $3,048 million and trading derivative liabilities of $3,086 million and $2,690 million at June 30, 2019 and December 31, 2018, respectively, as well as derivatives held for hedging and commitments accounted for as derivatives. See Note 9, "Derivative Financial Instruments," for additional information. Excluding changes in fair value of a derivative instrument associated with a qualifying cash flow hedge, which are recognized initially in other comprehensive income (loss), derivative assets and liabilities are recorded at fair value through net income

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

[5] Represents contingent consideration receivable associated with the sale of a portion of our PB business. Gains (losses) associated with this transaction are included in other income (loss) in the consolidated statement of income.

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