Accumulated Other Comprehensive Income (Loss) - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax (benefit) expense included in net unrealized gains (losses), investment securities	$ 245	$ 55
Tax included in reclassification, investment securities	(7)	(2)
Tax included in provision for credit losses, investment securities	0	0
Tax included in amortization, investment securities	1	1
Tax (benefit) expense included in net unrealized gains (losses), fair value option liabilities	128	(35)
Tax (benefit) expense included in net unrealized gains (losses), cash flow hedges	28	2
Tax included in reclassification, cash flow hedges	1	2
Tax included in net unrealized gains (losses), pension and postretirement benefit liability	$ 0	$ (1)
Accounting Standards Update 2016-13 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax on cumulative effect for AFS securities			$ 1	$ 0

Cumulative Effect of New Accounting Principle in Period of Adoption, Tax

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Other Comprehensive Income (Loss), Amortization of Unrealized Loss on Transfers from Available-for-Sale to Held-to Maturity Securities, Tax

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Amount of tax expense (benefit) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before reclassification, of tax expense (benefit) for gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount of tax expense (benefit) for reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount, before reclassification adjustment, of tax expense (benefit) for unrealized gain (loss) from increase (decrease) in instrument-specific credit risk on financial liability measured under fair value option.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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