Loans and Allowance for Loan Losses (Details 10) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Pre- and Post - modification recorded investments
Commitment to lend additional funds to borrowers with loan modifications classified as TDRs		$ 29	$ 98
Total excluding purchased credit-impaired loans	[1]	827	822
Commercial portfolio
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans		526	515
Commercial portfolio | Commercial and industrial
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans		509	499
Commercial portfolio | Commercial mortgage
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans		17	16
Consumer portfolio
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans		301	307
Consumer portfolio | Residential mortgage
Pre- and Post - modification recorded investments
Total excluding purchased credit-impaired loans		270	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|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmFjNDM2NWM5MjFiYTQzMWQ5ZDk1MGFiNmJhM2RiMzJifFRleHRTZWxlY3Rpb246QjcyRENBODlGMjNFQTFFNDhFNzIzODhDNkUyNUM2ODMM}