Fair Value of Financial Instruments Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of the beginning of the period	$ 119	$ 100
Net realized and unrealized losses (gains)	12	50
Transfers out of Level 3 to Level 2	0	2
Balance as of the end of the period	$ 131	$ 148