Loans and ACL - Summary of TDRs (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable [Line Items]
Total TDRs	$ 1,295	$ 1,232
ALLL attributable to TDRs	146	142
Performing TDRs
Financing Receivable [Line Items]
Total TDRs	1,119	1,043
Nonperforming TDRs (also included in NPL disclosures)
Financing Receivable [Line Items]
Total TDRs	176	189
Commercial | Commercial and industrial | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	65	50
Commercial | CRE | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	10	16
Retail | Residential mortgage | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	656	605
Retail | Direct | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	55	62
Retail | Indirect | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	305	281
Revolving credit | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	$ 28	$ 29