Allowance for Credit Losses - Allowance for Credit Losses and Liability for Off-balance Sheet Credit Exposures (Details) - USD ($) $ in Millions		Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020		Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Credit Loss [Abstract]
Loans		$ 475	$ 547	$ 1,015		$ 1,084	$ 1,192
Securities held-to-maturity	[1]	1		2
Other financial assets measured at amortized cost	[2]	2		2
Securities available-for-sale		1		1	[1]
Total allowance for credit losses		479		1,020
Liability for off-balance sheet credit exposures		$ 110	$ 128	$ 237			$ 253	$ 158

[1] See Note 5, "Securities," for additional information regarding the allowance for credit losses associated with our security portfolios.

[2] Primarily includes accrued interest receivables and customer acceptances.