Loans and ACL - Summary of TDRs (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 1,062	$ 1,295
ALLL attributable to TDRs	132	146
Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	980	1,119
Nonperforming TDRs (also included in NPL disclosures)
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	82	176
Commercial: | Commercial and industrial | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	47	65
Commercial: | CRE | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	6	8
Commercial: | Commercial construction | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	37	2
Consumer: | Residential Mortgage | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	470	656
Consumer: | Residential home equity and direct | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	51	56
Consumer: | Indirect auto | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	333	299
Consumer: | Indirect other | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	5	6
Credit card | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 31	$ 27