Investments (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2022 USD ($) security	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($)
Investments [Abstract]
Accrued interest receivable	$ 75	$ 65	$ 75
Transfer from available for sale to held-to-maturity, fair value	10,700	10,691
Investment securities available-for-sale transferred to held-to-maturity, at amortized cost (fair value $10,691)		0	$ 13,097	$ 0
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Transfer, Amount	13,100
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), before Tax	$ 2,400
Unrealized loss unamortized over the life of security		2,100
Unrealized loss unamortized over the life of security, after tax		$ 1,500
Number of AFS investment securities in an unrealized loss position | security	3,562	2,998	3,562
Allowance for credit loss on HTM securities (less than)		$ 1