Loans and Allowance for Loan Losses (Details 5) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Aging of loans
Current	$ 76,017	$ 76,013
30 to 89 Days Past Due	165	174
Total loans 90 days or more past due and still accruing	71	92
Total Past Due	236	266
Total loans held for investment, before purchased credit-impaired loans	76,253	76,279
Commercial portfolio
Aging of loans
Current	45,213	44,127
30 to 89 Days Past Due	47	42
Total loans 90 days or more past due and still accruing	13	16
Total Past Due	60	58
Total loans held for investment, before purchased credit-impaired loans	45,273	44,185
Commercial portfolio | Commercial and industrial
Aging of loans
Current	29,182	28,392
30 to 89 Days Past Due	21	19
Total loans 90 days or more past due and still accruing	7	12
Total Past Due	28	31
Total loans held for investment, before purchased credit-impaired loans	29,210	28,423
Commercial portfolio | Commercial mortgage
Aging of loans
Current	13,911	13,991
30 to 89 Days Past Due	26	21
Total loans 90 days or more past due and still accruing	6	4
Total Past Due	32	25
Total loans held for investment, before purchased credit-impaired loans	13,943	14,016
Commercial portfolio | Construction
Aging of loans
Current	2,120	1,744
30 to 89 Days Past Due	0	2
Total loans 90 days or more past due and still accruing	0	0
Total Past Due	0	2
Total loans held for investment, before purchased credit-impaired loans	2,120	1,746
Consumer portfolio
Aging of loans
Current	30,804	31,886
30 to 89 Days Past Due	118	132
Total loans 90 days or more past due and still accruing	58	76
Total Past Due	176	208
Total loans held for investment, before purchased credit-impaired loans	30,980	32,094
Consumer portfolio | Residential mortgage
Aging of loans
Current	27,702	28,802
30 to 89 Days Past Due	106	112
Total loans 90 days or more past due and still accruing	48	63
Total Past Due	154	175
Total loans held for investment, before purchased credit-impaired loans	27,856	28,977
Consumer portfolio | Home equity and other consumer loans
Aging of loans
Current	3,102	3,084
30 to 89 Days Past Due	12	20
Total loans 90 days or more past due and still accruing	10	13
Total Past Due	22	33
Total loans held for investment, before purchased credit-impaired loans	$ 3,124	$ 3,117