Loans and Allowance for Loan Losses (Details 10) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Pre- and Post - modification recorded investments
Commitment to lend additional funds to borrowers with loan modifications classified as TDRs	$ 48	$ 59
Total excluding purchased credit-impaired loans	637	599
Commercial portfolio
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	374	330
Commercial portfolio | Commercial and industrial
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	304	321
Commercial portfolio | Commercial mortgage
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	9	9
Commercial portfolio | Construction
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	61	0
Consumer portfolio
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	263	269
Consumer portfolio | Residential mortgage
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	234	239
Consumer portfolio | Home equity and other consumer loans
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	$ 29	$ 30