Loans and Allowance for Loan Losses (Details 10) - USD ($) $ in Millions	Sep. 30, 2016		Dec. 31, 2015
Pre- and Post - modification recorded investments
Commitment to lend additional funds to borrowers with loan modifications classified as TDRs	$ 59		$ 98
Total excluding purchased credit-impaired loans	690	[1]	822
Commercial portfolio
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	409		515
Commercial portfolio | Commercial and industrial
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	396		499
Commercial portfolio | Commercial mortgage
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	13		16
Consumer portfolio
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	281		307
Consumer portfolio | Residential mortgage
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	250		276
Consumer portfolio | Home equity and other consumer loans
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans	$ 31		$ 31

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmY5MzQwNzM1MzdkMTQzMGQ5MTUwNDQ0Nzg5ZDJmYTdhfFRleHRTZWxlY3Rpb246QTFGMjNCQTFCQUMzNThEREI3NDg4MTJBNjA4NDY1RjUM}