Loans and Allowance for Loan Losses (Details 12) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Troubled debt restructured loans
Minimum defaulting period	60 days
Total troubled debt restructured loans at date of default	$ 4	$ 3
Commercial portfolio
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	3	1
Commercial portfolio | Commercial and industrial
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	2	1
Commercial portfolio | Commercial mortgage
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	1
Consumer portfolio
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	1	2
Consumer portfolio | Residential mortgage
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	$ 1	$ 2