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Investment Securities - Additional Information (Details) - USD ($) $ in Millions			3 Months Ended		6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jan. 01, 2020
Debt Securities, Available-for-sale [Line Items]
Accrued interest receivable					$ 233
Proceeds from sales			$ 0	$ 909	144	$ 3,983
Debt Securities, Available-for-sale, Gain (Loss)				$ 15	1	$ 39
Derivative, collateral, obligation to return securities	$ 1	$ 1	1		1
Increase in retained earnings	35,361	40,340	35,361		35,361
Decrease in AOCI	$ (3,981)	$ (1,156)	(3,981)		(3,981)
Investment securities portfolio | US Treasury and Agency securities
Debt Securities, Available-for-sale [Line Items]
Percentage of portfolio	97.00%	96.00%
Collateral pledged
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, restricted	$ 12,600	$ 14,000	$ 12,600		$ 12,600
Cumulative effects from adoption of the CECL standard
Debt Securities, Available-for-sale [Line Items]
Increase in retained earnings							$ 11
Decrease in AOCI							$ 11

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