Securities - Narrative (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities transferred to held-to-maturity					$ 11,028	$ 0
Debt securities, available-for-sale and held-to-maturity, allowance for credit loss	$ 10	$ 11	$ 10		$ 10
AOCI, transfers from AFS to HTM Securities, gross unrealized losses	$ 80	$ 44
U.S. Treasury Securities And Agency Commercial MBS
Debt Securities, Available-for-sale [Line Items]
Transfers from available-for-sale to held-to-maturity securities, amortized cost			4,810	$ 5,950
Available-for-sale securities transferred to held-to-maturity			$ 5,080	$ 5,960