Loans and ACL - Summary of TDRs (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable [Line Items]
Total TDRs	$ 1,308	$ 1,295
ALLL attributable to TDRs	146	146
Performing TDRs
Financing Receivable [Line Items]
Total TDRs	1,130	1,119
Nonperforming TDRs (also included in NPL disclosures)
Financing Receivable [Line Items]
Total TDRs	178	176
Commercial | Commercial and industrial | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	63	65
Commercial | CRE | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	9	10
Retail | Residential mortgage | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	669	656
Retail | Direct | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	54	55
Retail | Indirect | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	306	305
Revolving credit | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	$ 29	$ 28