Investment Securities - Allowance for Credit Losses for HTM Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Beginning Balance (less than $1 million for 12/31/2020)	$ 7	$ 1
(Reduction of) Provision for credit losses	(1)	1
Ending Balance	6	$ 1
Accrued interest receivable	181		$ 171
Accrued interest receivable and other assets | Held-to-maturity Securities
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Accrued interest receivable	216		$ 225
Municipal bonds and notes
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Beginning Balance (less than $1 million for 12/31/2020)	1
Ending Balance	1
Corporate bonds
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Beginning Balance (less than $1 million for 12/31/2020)	6
Ending Balance	$ 5