Investment Securities - Additional Information (Details) $ in Millions	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Securities available for sale	$ 45,888	$ 46,150
Securities held to maturity	$ 36,503	36,771
Debt securities, available-for-sale, unrealized loss position, number of positions	1,130
Debt securities, available-for-sale, unrealized loss position, accumulated loss	$ 651	972
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	$ 634	675
Held-to-maturity, securities in unrealized loss positions, qualitative disclosure, number of positions	250
Debt securities, held-to-maturity, unrealized loss position, accumulated loss	$ 206
OTTI, credit losses recognized in earnings	140	140
Derivative, collateral, obligation to return securities	$ 1	$ 1
Investment securities portfolio \| US Treasury and Agency securities
Debt Securities, Available-for-sale [Line Items]
Percentage of portfolio	96.00%	96.00%
ASU 2017-12
Debt Securities, Available-for-sale [Line Items]
Securities held to maturity			$ 9,000
Collateral pledged
Debt Securities, Available-for-sale [Line Items]
Debt securities, held-to-maturity, restricted	$ 15,900	$ 16,300

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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