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, 2019	Dec. 31, 2018	Mar. 31, 2018
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Total lending-related commitments	$ 1,060,801	$ 1,039,258	$ 1,022,023
Total carrying value	1,401	1,409
Standby letters of credit and other financial guarantees
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Investment-grade	25,706	26,420
Noninvestment-grade	6,845	7,078
Total lending-related commitments	32,551	33,498
Allowance for lending-related commitments	189	167
Guarantee liability	343	354
Total carrying value	532	521
Commitments with collateral	17,476	17,400
Other letters of credit
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Investment-grade	1,797	2,079
Noninvestment-grade	1,006	746
Total lending-related commitments	2,803	2,825
Allowance for lending-related commitments	4	3
Guarantee liability	0	0
Total carrying value	4	3
Commitments with collateral	$ 605	$ 583