Loans and Allowance for Loan Losses - Aging of Balance of Loans Held for Investment By Class (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Aging of loans
Current	$ 84,237	$ 87,798
30 to 89 Days Past Due	509	283
90 Days or More Past Due	228	132
Total past due	737	415
Loans held for investment	84,974	88,213
Loans 90 days or more past due and still accruing	21	20
Commercial
Aging of loans
Current	49,555	45,610
30 to 89 Days Past Due	301	71
90 Days or More Past Due	125	64
Total past due	426	135
Loans held for investment	49,981	45,745
Loans 90 days or more past due and still accruing	6	3
Commercial | Construction
Aging of loans
Loans held for investment	1,550
Consumer
Aging of loans
Current	34,682	42,188
30 to 89 Days Past Due	208	212
90 Days or More Past Due	103	68
Total past due	311	280
Loans held for investment	34,993	42,468
Loans 90 days or more past due and still accruing	15	17
Residential mortgage and home equity | Consumer Loans
Aging of loans
Current	31,352	37,788
30 to 89 Days Past Due	180	179
90 Days or More Past Due	87	51
Total past due	267	230
Loans held for investment	31,619	38,018
Commercial mortgage | Commercial Loans
Aging of loans
Current	16,393	16,858
30 to 89 Days Past Due	134	34
90 Days or More Past Due	73	3
Total past due	207	37
Loans held for investment	16,600	16,895
Commercial and industrial | Commercial Loans
Aging of loans
Current	31,616	27,241
30 to 89 Days Past Due	163	37
90 Days or More Past Due	52	61
Total past due	215	98
Loans held for investment	31,831	27,339
Construction | Commercial Loans
Aging of loans
Current	1,546	1,511
30 to 89 Days Past Due	4	0
90 Days or More Past Due	0	0
Total past due	4	0
Loans held for investment	1,550	1,511
Other consumer | Consumer Loans
Aging of loans
Current	3,330	4,400
30 to 89 Days Past Due	28	33
90 Days or More Past Due	16	17
Total past due	44	50
Loans held for investment	$ 3,374	$ 4,450