Fair Value Measurements Changes in Fair Value Level 3 (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2016	Sep. 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		$ 6	$ 40
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		222	245
Other Segments and Holding Company [Member] | 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				$ 283	$ 229
Net realized and unrealized gains (losses)(1)	[1]	10	(40)
Purchases		50
Net transfers out		$ (121)	(44)
Trading Securities [Member] | Other Segments and Holding Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, [Roll Forward]
Purchases			$ 100

[1] Includes net unrealized losses of $6 million and $40 million for the nine months ended September 30, 2016 and 2015, respectively, relating to investments still held at September 30 of each respective period and which are included in net (loss) gain from investment activities in the condensed consolidated statements of operations.