Fair Value of Financial Instruments Unobservable Input Reconciliation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of the beginning of the period	$ 100	$ 139
Net realized and unrealized losses (gains)	50	(11)
Transfers out of Level 3 to Level 2	(2)	(3)
Balance as of the end of the period	$ 148	$ 131