Loans and ACL - Summary of TDRs (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 1,200	$ 1,062
ALLL attributable to TDRs	159	132
Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	1,079	980
Nonperforming TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	121	82
Commercial: | Commercial and industrial | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	65	47
Commercial: | CRE | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	7	6
Commercial: | Commercial construction | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	36	37
Commercial: | Lease financing | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	1	0
Consumer: | Residential Mortgage | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	513	470
Consumer: | Residential home equity and direct | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	66	51
Consumer: | Indirect auto | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	350	333
Consumer: | Indirect other | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	5	5
Consumer: | Student | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	1	0
Credit card | Performing TDRs
Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 35	$ 31