Loans and Allowance for Loan Losses (Details 12) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	$ 11	$ 11	$ 14	$ 18
Minimum defaulting period			60 days
Commercial portfolio
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	9	3	9	8
Commercial portfolio | Commercial and industrial
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	6	3	6	8
Commercial portfolio | Commercial mortgage
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	3		3
Consumer portfolio
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	2	8	5	10
Consumer portfolio | Residential mortgage
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	2	7	4	9
Consumer portfolio | Home equity and other consumer loans
Troubled debt restructured loans
Total troubled debt restructured loans at date of default		$ 1	$ 1	$ 1