Accumulated Other Comprehensive Loss - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax (benefit) expense included in net unrealized gains (losses), investment securities	$ 38	$ (46)	$ 166	$ (131)
Tax included in reclassification, investment securities	(11)	2	(18)	(2)
Tax included in amortization, investment securities	1	1	3	3
Tax (benefit) expense included in net unrealized gains (losses), fair value option liabilities	(1)	(15)	(34)	31
Tax (benefit) expense included in net unrealized gains (losses), cash flow hedges	(4)		(3)
Tax (benefit) expense included in net unrealized gains (losses), cash flow hedges (less than $1 million)		5		7
Tax included in reclassification, cash flow hedges	1		6
Tax included in reclassification, cash flow hedges		2		4
Tax included in net unrealized gains (losses), pension and postretirement benefit liability	$ 0	$ 0	$ (1)	$ 1
Unrealized Gains (Losses) on Investment Securities [Member] \| Accounting Standards Update 2016-01, Equity Investments Previously Classified as Available-for-sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption, tax					$ 0	$ 2

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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) of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount of tax expense (benefit), before reclassification adjustments, related to increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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