Off-balance Sheet Lending-related Financial Instruments, Guarantees, and Other Commitments - Standby Letters of Credit and Other Financial Guarantees (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Total lending-related commitments	$ 1,211,856	$ 1,165,688
Total carrying value	3,214	2,753
Standby letters of credit and other financial guarantees
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Investment-grade	26,608	22,850
Noninvestment-grade	8,165	8,132
Total lending-related commitments	34,773	30,982
Allowance for lending-related commitments	82	80
Guarantee liability	610	363
Total carrying value	692	443
Commitments with collateral	21,434	17,238
Other letters of credit
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Investment-grade	2,747	2,263
Noninvestment-grade	862	790
Total lending-related commitments	3,609	3,053
Allowance for lending-related commitments	29	14
Guarantee liability	0	0
Total carrying value	29	14
Commitments with collateral	$ 879	$ 498