Investment Securities (Details 1) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	$ 467	$ 451
Estimated Fair Value, 12 months or more	32	32
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(7)	(19)
Gross Unrealized Losses, 12 months or more	(2)	(2)
U.S. States and Political Subdivisions Debt Securities [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	101	153
Estimated Fair Value, 12 months or more	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(2)	(11)
Gross Unrealized Losses, 12 months or more	0	0
U.S. Government agency obligations [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	366	298
Estimated Fair Value, 12 months or more	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(5)	(8)
Gross Unrealized Losses, 12 months or more	0	0
Other [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	0	0
Estimated Fair Value, 12 months or more	32	32
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	0	0
Gross Unrealized Losses, 12 months or more	$ (2)	$ (2)