Loans and Allowance for Loan Losses - Balance of Loans Held for Investment, by Class (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Aging of loans
Current	$ 86,151	$ 79,687
30 to 89 Days Past Due	258	207
90 Days or More Past Due	98	120
Total Past Due	356	327
Total	86,507	80,014
Loans still accruing	23	12
Commercial
Aging of loans
Current	43,040	40,807
30 to 89 Days Past Due	55	33
90 Days or More Past Due	40	69
Total Past Due	95	102
Total	43,135	40,909
Commercial | Commercial and industrial
Aging of loans
Current	26,114	24,734
30 to 89 Days Past Due	18	17
90 Days or More Past Due	36	63
Total Past Due	54	80
Total	26,168	24,814
Commercial | Commercial mortgage
Aging of loans
Current	15,333	14,298
30 to 89 Days Past Due	17	16
90 Days or More Past Due	4	6
Total Past Due	21	22
Total	15,354	14,320
Commercial | Construction
Aging of loans
Current	1,593	1,775
30 to 89 Days Past Due	20	0
90 Days or More Past Due	0	0
Total Past Due	20	0
Total	1,613	1,775
Consumer
Aging of loans
Current	43,111	38,880
30 to 89 Days Past Due	203	174
90 Days or More Past Due	58	51
Total Past Due	261	225
Total	43,372	39,105
Consumer | Residential mortgage
Aging of loans
Current	38,218	35,453
30 to 89 Days Past Due	175	151
90 Days or More Past Due	46	39
Total Past Due	221	190
Total	38,439	35,643
Consumer | Home equity and other consumer loans
Aging of loans
Current	4,893	3,427
30 to 89 Days Past Due	28	23
90 Days or More Past Due	12	12
Total Past Due	40	35
Total	$ 4,933	$ 3,462