Off-balance Sheet Lending-related Financial Instruments, Guarantees, and Other Commitments - Standby Letters of Credit and Other Financial Guarantees (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Total lending-related commitments	$ 1,095,090	$ 1,039,258	$ 1,048,674
Total carrying value	1,555	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	27,131	26,420
Noninvestment-grade	6,958	7,078
Total lending-related commitments	34,089	33,498
Allowance for lending-related commitments	215	167
Guarantee liability	390	354
Total carrying value	605	521
Commitments with collateral	17,690	17,400
Other letters of credit
Standby letters of credit and other financial guarantees and other letters of credit [Abstract]
Investment-grade	3,249	2,079
Noninvestment-grade	949	746
Total lending-related commitments	4,198	2,825
Allowance for lending-related commitments	5	3
Guarantee liability	0	0
Total carrying value	5	3
Commitments with collateral	$ 877	$ 583