Fair Value Measurements Changes in Fair Value Level 3 (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, [Roll Forward]
Unrealized gain included in earnings related to Level 3 assets still held at period end		$ 0	$ 26
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, [Roll Forward]
Fair value of investments measured at fair value on a recurring basis		223	252	$ 283	$ 229
Net realized and unrealized gains (losses)(1)	[1]	10	(43)
Purchases		50	100
Net transfers out		$ (120)	$ (34)

[1] Includes unrealized gains of zero for the six months ended June 30, 2016 and unrealized losses of $26 million for the six months ended June 30, 2015 relating to investments still held at June 30 of each respective period and which are included in net (loss) gain from investment activities in the condensed consolidated statements of operations.