Asset Quality (Impaired Loans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Unpaid Principal Balance - Impaired Financing Receivable [Abstract]
Unpaid principal balance - Impaired loans with an associated allowance	$ 1,303	$ 1,641
Unpaid principal balance - Impaired loans without an associated allowance	1,455	1,513
Unpaid principal balance - Total impaired loans	2,758	3,154
Recorded Investment - Impaired Financing Receivable [Abstract]
Recorded investment - Impaired loans with an associated allowance	1,132	1,367
Recorded investment - Impaired loans without an associated allowance	951	1,004
Recorded investment - Total impaired loans	2,083	2,371
Associated Allowance - Total impaired loans	209	271
Average Recorded Receivable - Impaired Financing Receivable [Abstract]
Average recorded investment - Impaired loans with an associated allowance	1,253	1,491
Average recorded investment - Impaired loans without an associated allowance	939	978
Average recorded investment - Total impaired loans	2,192	2,469
Total commercial lending
Unpaid Principal Balance - Impaired Financing Receivable [Abstract]
Unpaid principal balance - Impaired loans with an associated allowance	440	580
Unpaid principal balance - Impaired loans without an associated allowance	413	494
Recorded Investment - Impaired Financing Receivable [Abstract]
Recorded investment - Impaired loans with an associated allowance	315	353
Recorded investment - Impaired loans without an associated allowance	326	366
Associated Allowance - Total impaired loans	73	76
Average Recorded Receivable - Impaired Financing Receivable [Abstract]
Average recorded investment - Impaired loans with an associated allowance	349	419
Average recorded investment - Impaired loans without an associated allowance	294	330
Total consumer lending
Unpaid Principal Balance - Impaired Financing Receivable [Abstract]
Unpaid principal balance - Impaired loans with an associated allowance	863	1,061
Unpaid principal balance - Impaired loans without an associated allowance	1,042	1,019
Recorded Investment - Impaired Financing Receivable [Abstract]
Recorded investment - Impaired loans with an associated allowance	817	1,014
Recorded investment - Impaired loans without an associated allowance	625	638
Associated Allowance - Total impaired loans	136	195
Average Recorded Receivable - Impaired Financing Receivable [Abstract]
Average recorded investment - Impaired loans with an associated allowance	904	1,072
Average recorded investment - Impaired loans without an associated allowance	$ 645	$ 648