Asset Quality (Impaired Loans) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Unpaid Principal Balance - Impaired Financing Receivable [Abstract]
Unpaid principal balance - Impaired loans with an associated allowance	$ 1,354	$ 1,303
Unpaid principal balance - Impaired loans without an associated allowance	1,365	1,455
Unpaid principal balance - Total impaired loans	2,719	2,758
Recorded Investment - Impaired Financing Receivable [Abstract]
Recorded investment - Impaired loans with an associated allowance	1,173	1,132
Recorded investment - Impaired loans without an associated allowance	891	951
Recorded investment - Total impaired loans	2,064	2,083
Associated Allowance - Total impaired loans	209	209
Average Recorded Receivable - Impaired Financing Receivable [Abstract]
Average recorded investment - Impaired loans with an associated allowance	1,165	1,253
Average recorded investment - Impaired loans without an associated allowance	903	939
Average recorded investment - Total impaired loans	2,068	2,192
Total commercial lending [Member]
Unpaid Principal Balance - Impaired Financing Receivable [Abstract]
Unpaid principal balance - Impaired loans with an associated allowance	530	440
Unpaid principal balance - Impaired loans without an associated allowance	358	413
Recorded Investment - Impaired Financing Receivable [Abstract]
Recorded investment - Impaired loans with an associated allowance	396	315
Recorded investment - Impaired loans without an associated allowance	287	326
Associated Allowance - Total impaired loans	86	73
Average Recorded Receivable - Impaired Financing Receivable [Abstract]
Average recorded investment - Impaired loans with an associated allowance	365	349
Average recorded investment - Impaired loans without an associated allowance	292	294
Total consumer lending [Member]
Unpaid Principal Balance - Impaired Financing Receivable [Abstract]
Unpaid principal balance - Impaired loans with an associated allowance	824	863
Unpaid principal balance - Impaired loans without an associated allowance	1,007	1,042
Recorded Investment - Impaired Financing Receivable [Abstract]
Recorded investment - Impaired loans with an associated allowance	777	817
Recorded investment - Impaired loans without an associated allowance	604	625
Associated Allowance - Total impaired loans	123	136
Average Recorded Receivable - Impaired Financing Receivable [Abstract]
Average recorded investment - Impaired loans with an associated allowance	800	904
Average recorded investment - Impaired loans without an associated allowance	$ 611	$ 645