Investment Securities (Details 2) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2016 USD ($) securities	Dec. 31, 2015 USD ($) securities
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months | securities	0	52
Number of securities, 12 months or more | securities	24	17
Number of securities, total | securities	24	69
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	$ 0	$ 450
Estimated Fair Value, 12 months or more	36	46
Estimated Fair Value, Total	36	496
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	0	(5)
Gross Unrealized Losses, 12 months or more	(1)	(4)
Gross Unrealized Losses, Total	$ (1)	$ (9)
Ratio Of Fair Value To Amortized Cost Between Ninety And One Hundred Percent [Member]
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months | securities	0	52
Number of securities, 12 months or more | securities	24	15
Number of securities, total | securities	24	67
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	$ 0	$ 450
Estimated Fair Value, 12 months or more	36	37
Estimated Fair Value, Total	36	487
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	0	(5)
Gross Unrealized Losses, 12 months or more	(1)	(2)
Gross Unrealized Losses, Total	$ (1)	$ (7)
Ratio Of Fair Value To Amortized Cost Less Than Ninety Percent [Member]
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months | securities	0	0
Number of securities, 12 months or more | securities	0	2
Number of securities, total | securities	0	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	$ 0	$ 0
Estimated Fair Value, 12 months or more	0	9
Estimated Fair Value, Total	0	9
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	0	(2)
Gross Unrealized Losses, Total	$ 0	$ (2)