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	Sep. 30, 2012	Dec. 31, 2011
Without hedge designation [Member]
Contractual/notional amount	$ 97	$ 46
Estimated fair value asset		1
Estimated fair value (liability)	(3)	(1)
Without hedge designation [Member] | Credit default swaps - purchased protection [Member]
Contractual/notional amount	20	20
Estimated fair value asset
Estimated fair value (liability)	(1)	(1)
Without hedge designation [Member] | Currency forwards [Member]
Contractual/notional amount	72	22
Estimated fair value asset		1
Estimated fair value (liability)	(2)
Without hedge designation [Member] | Equity warrants [Member]
Contractual/notional amount	5	4
Estimated fair value asset
Estimated fair value (liability)