Fair Value of Financial Instruments Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of the beginning of the period	$ 131	$ 100	$ 119	$ 100
Net realized and unrealized losses (gains)	28	20	40	70
Transfers out of Level 3 to Level 2	(1)	0	(1)	2
Balance as of the end of the period	$ 158	$ 148	$ 158	$ 168