Loans and ACL - Summary of TDRs (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable [Line Items]
Total TDRs	$ 1,205	$ 1,295
ALLL attributable to TDRs	149	146
Performing TDRs
Financing Receivable [Line Items]
Total TDRs	1,070	1,119
Nonperforming TDRs (also included in NPL disclosures)
Financing Receivable [Line Items]
Total TDRs	135	176
Commercial | Commercial and industrial | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	84	65
Commercial | CRE | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	8	10
Retail | Residential mortgage | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	581	656
Retail | Direct | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	53	55
Retail | Indirect | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	315	305
Revolving credit | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	$ 29	$ 28