Loans and Allowance for Loan Losses (Details 5) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Aging of loans
Current	$ 78,151	$ 77,188
30 to 89 Days Past Due	159	228
Total loans 90 days or more past due and still accruing	124	135
Total Past Due	283	363
Total loans held for investment, before purchased credit-impaired loans	78,434	77,551
Commercial portfolio
Aging of loans
Current	43,792	43,939
30 to 89 Days Past Due	28	91
Total loans 90 days or more past due and still accruing	69	76
Total Past Due	97	167
Total loans held for investment, before purchased credit-impaired loans	43,889	44,106
Commercial portfolio | Commercial and industrial
Aging of loans
Current	27,317	27,085
30 to 89 Days Past Due	10	54
Total loans 90 days or more past due and still accruing	54	59
Total Past Due	64	113
Total loans held for investment, before purchased credit-impaired loans	27,381	27,198
Commercial portfolio | Commercial mortgage
Aging of loans
Current	14,435	14,571
30 to 89 Days Past Due	18	37
Total loans 90 days or more past due and still accruing	15	17
Total Past Due	33	54
Total loans held for investment, before purchased credit-impaired loans	14,468	14,625
Commercial portfolio | Construction
Aging of loans
Current	2,040	2,283
30 to 89 Days Past Due	0	0
Total loans 90 days or more past due and still accruing	0	0
Total Past Due	0	0
Total loans held for investment, before purchased credit-impaired loans	2,040	2,283
Consumer portfolio
Aging of loans
Current	34,359	33,249
30 to 89 Days Past Due	131	137
Total loans 90 days or more past due and still accruing	55	59
Total Past Due	186	196
Total loans held for investment, before purchased credit-impaired loans	34,545	33,445
Consumer portfolio | Residential mortgage
Aging of loans
Current	31,012	29,770
30 to 89 Days Past Due	110	110
Total loans 90 days or more past due and still accruing	40	42
Total Past Due	150	152
Total loans held for investment, before purchased credit-impaired loans	31,162	29,922
Consumer portfolio | Home equity and other consumer loans
Aging of loans
Current	3,347	3,479
30 to 89 Days Past Due	21	27
Total loans 90 days or more past due and still accruing	15	17
Total Past Due	36	44
Total loans held for investment, before purchased credit-impaired loans	$ 3,383	$ 3,523