Financial Derivatives (Credit Ratings of Credit Default Swaps) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Notional Amount of Credit Risk Derivatives	$ 110		$ 304
Underlying Other Guarantor [Member]
Notional Amount of Credit Risk Derivatives	0	[1]	94	[1]
Underlying Other Guarantor [Member] | External Credit Rating, Investment Grade [Member]
Notional Amount of Credit Risk Derivatives	0	[1],[2]	84	[1],[2]
Underlying Other Guarantor [Member] | External Credit Rating, Non Investment Grade [Member]
Notional Amount of Credit Risk Derivatives	0	[1],[2],[3]	10	[1],[2],[3]
Underlying Other Beneficiary [Member]
Notional Amount of Credit Risk Derivatives	110		210
Underlying Other Beneficiary [Member] | External Credit Rating, Investment Grade [Member]
Notional Amount of Credit Risk Derivatives	95	[2]	145	[2]
Underlying Other Beneficiary [Member] | External Credit Rating, Non Investment Grade [Member]
Notional Amount of Credit Risk Derivatives	$ 15	[3]	$ 65	[3]

[1] There were no credit default swaps sold as of September 30, 2012.

[2] Investment grade with a rating of BBB-/Baa3 or above based on published rating agency information.

[3] Subinvestment grade with a rating below BBB-/Baa3 based on published rating agency information.