Loans and Allowance for Loan Losses (Details 12) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Troubled debt restructured loans
Minimum defaulting period			60 days
Total troubled debt restructured loans at date of default	$ 17	$ 12	$ 21	$ 15
Commercial portfolio
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	17	10	20	11
Commercial portfolio | Commercial and industrial
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	17	10	19	11
Commercial portfolio | Commercial mortgage
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	0		1
Consumer portfolio
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	0	2	1	4
Consumer portfolio | Residential mortgage
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	$ 0	1	$ 1	3
Consumer portfolio | Home equity and other consumer loans
Troubled debt restructured loans
Total troubled debt restructured loans at date of default		$ 1		$ 1