Loans and ACL - Summary of Nonperforming Assets and Residential Mortgage Loans in the Process of Foreclosure (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
Nonperforming	$ 1,034	$ 454
Other Real Estate, Foreclosed Assets, and Repossessed Assets	63	82
Total nonperforming assets	1,177	684
Residential mortgage loans in the process of foreclosure	300	409
LHFS
Financing Receivable, Impaired [Line Items]
Nonperforming	41	107
Other Property [Member]
Financing Receivable, Impaired [Line Items]
Other Real Estate, Foreclosed Assets, and Repossessed Assets	$ 39	$ 41