Loans and ACL - Summary of Nonperforming Assets and Residential Mortgage Loans in the Process of Foreclosure (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Nonperforming	$ 454	$ 522
Other Real Estate, Foreclosed Assets, and Repossessed Assets	82	35
Identifiable assets (period end)	473,078	225,697
Residential mortgage loans in the process of foreclosure	409	253
LHFS
Financing Receivable, Impaired [Line Items]
Nonperforming	107	0
Nonperforming TDRs (also included in NPL disclosures)
Financing Receivable, Impaired [Line Items]
Identifiable assets (period end)	684	585
Other Property [Member]
Financing Receivable, Impaired [Line Items]
Other Real Estate, Foreclosed Assets, and Repossessed Assets	$ 41	$ 28