Investments (Other Trading Account Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Amortized Cost	$ 3,385		$ 2,274
Fair Value	5,545		4,225
Cash Equivalents And Short Term Investments [Member]
Amortized Cost	4		3
Fair Value	3		3
US Government Corporations and Agencies Securities [Member]
Amortized Cost	41		212
Fair Value	31		214
Foreign Government Debt Securities [Member]
Amortized Cost	47		25
Fair Value	47		25
Corporate Securities [Member]
Amortized Cost	557		319
Fair Value	555		318
Asset-backed Securities [Member]
Amortized Cost	698		706
Fair Value	652		661
Residential Mortgage Backed Securities [Member]
Amortized Cost	186		301
Fair Value	96		181
Commercial Mortgage Backed Securities [Member]
Amortized Cost	155		144
Fair Value	110		103
Fixed Maturities [Member]
Amortized Cost	1,684		1,707
Fair Value	1,491		1,502
Equity Securities [Member]
Amortized Cost	1,682	[1]	548
Fair Value	1,621	[1]	561
Other Assets [Member]
Amortized Cost	15		16
Fair Value	19		20
Derivative Financial Instruments, Assets [Member]
Fair Value	2,411		2,139
Investments Excluding Derivative Instruments [Member]
Amortized Cost	3,385		2,274
Fair Value	$ 3,134		$ 2,086

[1] During 2011, perpetual preferred stocks of $1.3 billion were reclassified from “Equity securities, available-for-sale.” Additionally, $17 million of gains were reclassified from “Accumulated other comprehensive income (loss)” into “Asset management fees and other income.” Prior periods were not restated.