Asset Quality (Impaired Loans) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Unpaid Principal Balance - Impaired Financing Receivable [Abstract]
Unpaid principal balance - Impaired loans with an associated allowance	$ 1,225	$ 1,303
Unpaid principal balance - Impaired loans without an associated allowance	1,405	1,455
Unpaid principal balance - Total impaired loans	2,630	2,758
Recorded Investment - Impaired Financing Receivable [Abstract]
Recorded investment - Impaired loans with an associated allowance	1,072	1,132
Recorded investment - Impaired loans without an associated allowance	956	951
Recorded investment - Total impaired loans	2,028	2,083
Associated Allowance - Total impaired loans	176	209
Average Recorded Receivable - Impaired Financing Receivable [Abstract]
Average recorded investment - Impaired loans with an associated allowance	1,142	1,253
Average recorded investment - Impaired loans without an associated allowance	917	939
Average recorded investment - Total impaired loans	2,059	2,192
Total commercial lending [Member]
Unpaid Principal Balance - Impaired Financing Receivable [Abstract]
Unpaid principal balance - Impaired loans with an associated allowance	491	440
Unpaid principal balance - Impaired loans without an associated allowance	360	413
Recorded Investment - Impaired Financing Receivable [Abstract]
Recorded investment - Impaired loans with an associated allowance	375	315
Recorded investment - Impaired loans without an associated allowance	310	326
Associated Allowance - Total impaired loans	81	73
Average Recorded Receivable - Impaired Financing Receivable [Abstract]
Average recorded investment - Impaired loans with an associated allowance	367	349
Average recorded investment - Impaired loans without an associated allowance	297	294
Total consumer lending [Member]
Unpaid Principal Balance - Impaired Financing Receivable [Abstract]
Unpaid principal balance - Impaired loans with an associated allowance	734	863
Unpaid principal balance - Impaired loans without an associated allowance	1,045	1,042
Recorded Investment - Impaired Financing Receivable [Abstract]
Recorded investment - Impaired loans with an associated allowance	697	817
Recorded investment - Impaired loans without an associated allowance	646	625
Associated Allowance - Total impaired loans	95	136
Average Recorded Receivable - Impaired Financing Receivable [Abstract]
Average recorded investment - Impaired loans with an associated allowance	775	904
Average recorded investment - Impaired loans without an associated allowance	$ 620	$ 645