Loans and ACL - Summary of TDRs (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable [Line Items]
Total TDRs	$ 1,238	$ 1,232
ALLL attributable to TDRs	145	142
Performing TDRs
Financing Receivable [Line Items]
Total TDRs	1,042	1,043
Nonperforming TDRs (also included in NPL disclosures)
Financing Receivable [Line Items]
Total TDRs	196	189
Commercial | Commercial and industrial | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	38	50
Commercial | CRE | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	12	16
Commercial | Lease financing | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	0	0
Retail | Residential mortgage | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	627	605
Retail | Direct | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	59	62
Retail | Indirect | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	277	281
Revolving credit | Performing TDRs
Financing Receivable [Line Items]
Total TDRs	$ 29	$ 29