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, 2013	Dec. 31, 2012
Summary of Derivative Instruments Without Hedge Designation
Contractual/notional amount	$ 146	$ 84
Estimated fair value asset	1
Estimated fair value (liability)	(1)	(3)
Credit default swap - 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	43	59
Estimated fair value asset	1
Estimated fair value (liability)		(2)
Forward commitments for mortgage-backed securities [Member]
Summary of Derivative Instruments Without Hedge Designation
Contractual/notional amount	78
Estimated fair value asset
Estimated fair value (liability)
Equity warrants [Member]
Summary of Derivative Instruments Without Hedge Designation
Contractual/notional amount	5	5
Estimated fair value asset
Estimated fair value (liability)