Off-balance Sheet Lending-related Financial Instruments, Guarantees, and Other Commitments - Standby Letters of Credit and Other Financial Guarantees (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Total lending-related commitments	$ 1,079,762	$ 1,039,258	$ 1,045,993
Total carrying value	1,473	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	25,041	26,420
Noninvestment-grade	7,155	7,078
Total lending-related commitments	32,196	33,498
Allowance for lending-related commitments	210	167
Guarantee liability	344	354
Total carrying value	554	521
Commitments with collateral	17,373	17,400
Other letters of credit
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Investment-grade	2,181	2,079
Noninvestment-grade	1,142	746
Total lending-related commitments	3,323	2,825
Allowance for lending-related commitments	3	3
Guarantee liability	0	0
Total carrying value	3	3
Commitments with collateral	$ 768	$ 583