Fair Value of Financial Instruments Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of the beginning of the period	$ 168	$ 89	$ 100	$ 139
Net realized and unrealized losses (gains)	15	9	85	(45)
Settlements	0	(1)	0	(1)
Transfers out of Level 3 to Level 2	(14)	1	(16)	(5)
Balance as of the end of the period	$ 169	$ 98	$ 169	$ 98