Loans and Allowance for Loan Losses (Details 13) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Loan impairment
Recorded investment with an allowance	$ 439	$ 360
Recorded investment without an allowance	181	266
Impaired loans	620	626
Allowance for impaired loans	50	42
Unpaid principal balance with an allowance	513	388
Unpaid principal balance without an allowance	166	314
Total, excluding purchased credit impaired loans
Loan impairment
Recorded investment with an allowance	437	360
Recorded investment without an allowance	179	262
Impaired loans	616	622
Allowance for impaired loans	50	42
Unpaid principal balance with an allowance	511	387
Unpaid principal balance without an allowance	159	300
Commercial portfolio
Loan impairment
Recorded investment with an allowance	231	171
Recorded investment without an allowance	59	159
Impaired loans	290	330
Allowance for impaired loans	32	24
Unpaid principal balance with an allowance	291	185
Unpaid principal balance without an allowance	11	172
Commercial portfolio | Commercial and industrial
Loan impairment
Recorded investment with an allowance	202	156
Recorded investment without an allowance	45	64
Impaired loans	247	220
Allowance for impaired loans	29	24
Unpaid principal balance with an allowance	242	167
Unpaid principal balance without an allowance	11	64
Commercial portfolio | Commercial mortgage
Loan impairment
Recorded investment with an allowance	27	15
Recorded investment without an allowance	14	60
Impaired loans	41	75
Allowance for impaired loans	3
Unpaid principal balance with an allowance	46	18
Unpaid principal balance without an allowance		70
Commercial portfolio | Construction
Loan impairment
Recorded investment with an allowance	2
Recorded investment without an allowance		35
Impaired loans	2	35
Unpaid principal balance with an allowance	3
Unpaid principal balance without an allowance		38
Consumer portfolio
Loan impairment
Recorded investment with an allowance	206	189
Recorded investment without an allowance	120	103
Impaired loans	326	292
Allowance for impaired loans	18	18
Unpaid principal balance with an allowance	220	202
Unpaid principal balance without an allowance	148	128
Consumer portfolio | Residential mortgage
Loan impairment
Recorded investment with an allowance	203	186
Recorded investment without an allowance	100	85
Impaired loans	303	271
Allowance for impaired loans	18	18
Unpaid principal balance with an allowance	217	199
Unpaid principal balance without an allowance	114	97
Consumer portfolio | Home equity and other consumer loans
Loan impairment
Recorded investment with an allowance	3	3
Recorded investment without an allowance	20	18
Impaired loans	23	21
Unpaid principal balance with an allowance	3	3
Unpaid principal balance without an allowance	34	31
Purchased credit-impaired loans
Loan impairment
Recorded investment with an allowance	2
Recorded investment without an allowance	2	4
Impaired loans	4	4
Unpaid principal balance with an allowance	2	1
Unpaid principal balance without an allowance	$ 7	$ 14