Derivative Financial Instruments (Summary of aggregate contractual or notional amounts and gross estimated fair values related to derivative financial instruments) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Summary of Derivative Instruments Without Hedge Designation
Contractual/notional amount	$ 57	$ 46
Estimated fair value asset		1
Estimated fair value (liability)	(2)	(1)
Credit default swaps - purchased protection [Member]
Summary of Derivative Instruments Without Hedge Designation
Contractual/notional amount	20	20
Estimated fair value asset
Estimated fair value (liability)	(1)	(1)
Currency forwards [Member]
Summary of Derivative Instruments Without Hedge Designation
Contractual/notional amount	33	22
Estimated fair value asset		1
Estimated fair value (liability)	(1)
Equity warrants [Member]
Summary of Derivative Instruments Without Hedge Designation
Contractual/notional amount	4	4
Estimated fair value asset
Estimated fair value (liability)