Fair Value of Financial Instruments Unobservable Input Reconciliation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of the beginning of the period	$ 56	$ 88	$ 16	$ 79
Net realized and unrealized losses (1)	8	(7)	48	4
Purchases	0	(2)	0	(2)
Issuances	0	0	0	(1)
Transfers out of Level 3 to Level 2	0	0	0	(1)
Balance as of the end of the period	$ 64	$ 79	$ 64	$ 79