Loans and Allowance for Loan Losses (Details 11) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	[1]	$ 144	$ 60
Post-Modification Outstanding Recorded Investment	[2]	144	60
Commercial portfolio
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	[1]	140	55
Post-Modification Outstanding Recorded Investment	[2]	140	55
Commercial portfolio | Commercial and industrial
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	[1]	78	50
Post-Modification Outstanding Recorded Investment	[2]	78	50
Commercial portfolio | Commercial mortgage
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	[1]	1	5
Post-Modification Outstanding Recorded Investment	[2]	1	5
Commercial portfolio | Construction
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	[1]	61
Post-Modification Outstanding Recorded Investment	[2]	61
Consumer portfolio
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	[1]	4	5
Post-Modification Outstanding Recorded Investment	[2]	4	5
Consumer portfolio | Residential mortgage
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	[1]	4	4
Post-Modification Outstanding Recorded Investment	[2]	$ 4	4
Consumer portfolio | Home equity and other consumer loans
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	[1]		1
Post-Modification Outstanding Recorded Investment	[2]		$ 1

[1] Represents the recorded investment in the loan immediately prior to the restructuring event.

[2] Represents the recorded investment in the loan immediately following the restructuring event. It includes the effect of paydowns that were required as part of the restructuring terms.