Loans and Allowance for Loan Losses - Recorded Investment Amounts of TDRs at Date of Default (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	$ 63	$ 32
Minimum defaulting period	60 days
Commercial
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	$ 57	28
Commercial | Commercial and industrial
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	57	25
Commercial | Commercial mortgage
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	0	3
Consumer
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	6	4
Consumer | Residential mortgage
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	4	4
Consumer | Home equity and other consumer loans
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	$ 2	$ 0