Off-balance Sheet Lending-related Financial Instruments, Guarantees, and Other Commitments - Standby Letters of Credit, Other Financial Guarantees and Other Letters of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Total lending-related commitments	$ 1,165,688	$ 1,108,399
Total carrying value	2,753	1,586
Standby letters of credit and other financial guarantees
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Investment-grade	22,850	26,880
Noninvestment-grade	8,132	7,362
Total lending-related commitments	30,982	34,242
Allowance for lending-related commitments	80	216
Guarantee liability	363	402
Total carrying value	443	618
Commitments with collateral	17,238	17,853
Other letters of credit
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Investment-grade	2,263	2,137
Noninvestment-grade	790	824
Total lending-related commitments	3,053	2,961
Allowance for lending-related commitments	14	4
Guarantee liability	0	0
Total carrying value	14	4
Commitments with collateral	$ 498	$ 728