Investments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Schedule of Trading Securities [Line Items]
Trading Securities, Debt	$ 51		$ 51		$ 57
Trading Securities, Equity	65		65		63
Trading Securities, Total	116		116		$ 120
Trading Securities, Recognized Gain	2	$ 0	7	$ 0
Trading Securities, Recognized (Loss)	0	(2)	(4)	(2)
Trading Securities, Recognized Net Gain (Loss)	$ 2	$ (2)	$ 3	$ (2)