Investments (Narrative) (Details) $ in Millions	Mar. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Debt and Equity Securities, FV-NI [Line Items]
Accrued interest receivable	$ 199	$ 200
Number of HTM investment securities in an unrealized loss position | security	162	119
Number of AFS investment securities in an unrealized loss position | security	1,062	549
Allowance for credit loss on HTM securities (less than)	$ 1
Carrying value of pledged securities	2,100	$ 2,300
Securities Investment
Debt and Equity Securities, FV-NI [Line Items]
Accrued interest receivable	$ 51	$ 54