Investments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Schedule of Trading Securities [Line Items]
Trading Securities, Debt	$ 48		$ 48		$ 57
Trading Securities, Equity	59		59		63
Trading Securities, Total	107		107		$ 120
Trading Securities, Recognized Gain	4	$ 1	11	$ 1
Trading Securities, Recognized (Loss)	0	(6)	(4)	(8)
Trading Securities, Recognized Net Gain (Loss)	$ 4	$ (5)	$ 7	$ (7)