Fair Value Significant unobservable inputs (Level 3) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets Liabilites Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning of Period	$ 7	$ 19
Total gains (losses), Included in earnings	(1)	(2)
Total gains (losses), Included in other comprehensive income	(1)	(12)
Purchases	3	5
Settlements	(5)	(3)
End of Period	3	7
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or (losses) relating to assets held at the reporting date	$ 0	$ (2)
Minimum [Member]
Fair Value, Assets Liabilites Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Volatility rate	26.00%
Maximum [Member]
Fair Value, Assets Liabilites Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Volatility rate	27.00%