Loans and Allowance for Loan Losses - Balance of Loans Held for Investment, by Class (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Aging of loans
Current	$ 87,798	$ 86,151
30 to 89 Days Past Due	283	258
90 Days or More Past Due	132	98
Total Past Due	415	356
Loans still accruing	20	23
Loans held for investment	88,213	86,507
Commercial | Commercial and industrial
Aging of loans
Current	27,241	26,114
30 to 89 Days Past Due	37	18
90 Days or More Past Due	61	36
Total Past Due	98	54
Loans held for investment	27,339	26,168
Commercial | Commercial mortgage
Aging of loans
Current	16,858	15,333
30 to 89 Days Past Due	34	17
90 Days or More Past Due	3	4
Total Past Due	37	21
Loans held for investment	16,895	15,354
Commercial | Construction
Aging of loans
Current	1,511	1,593
30 to 89 Days Past Due	0	20
90 Days or More Past Due	0	0
Total Past Due	0	20
Loans held for investment	1,511	1,613
Consumer | Other Consumer Loans [Member]
Aging of loans
Current	4,400	2,671
30 to 89 Days Past Due	33	15
90 Days or More Past Due	17	9
Total Past Due	50	24
Loans held for investment	4,450	2,695
Consumer | residential mortgage and home equity [Member]
Aging of loans
Current	37,788	40,440
30 to 89 Days Past Due	179	188
90 Days or More Past Due	51	49
Total Past Due	230	237
Loans held for investment	38,018	40,677
Consumer Portfolio Segment [Member]
Aging of loans
Current	42,188	43,111
30 to 89 Days Past Due	212	203
90 Days or More Past Due	68	58
Total Past Due	280	261
Total	42,465	43,366
Loans held for investment	42,468	43,372
Consumer Portfolio Segment [Member] | residential mortgage and home equity [Member]
Aging of loans
Total	38,015	40,671
Commercial Portfolio Segment [Member]
Aging of loans
Current	45,610	43,040
30 to 89 Days Past Due	71	55
90 Days or More Past Due	64	40
Total Past Due	135	95
Loans held for investment	$ 45,745	$ 43,135