Investments (Details 5) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	$ 236		$ 128		$ 163
Realized - impairments	(26)		(52)		(62)
Fixed maturities [Member]
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	55		68		146
Realized - impairments	(9)		(57)		(79)
Change in unrealized	790		407		751
Equity securities [Member]
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	192		88		36
Realized - impairments	(24)		(6)		(1)
Change in unrealized	(23)		(48)		49
Mortgage Loans and Other Investments [Member]
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(3)		(24)		(5)
Realized - impairments			(5)		(6)
Other [Member]
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(8)	[1]	(4)	[1]	(14)	[1]
Realized - impairments	7	[1]	16	[1]	24	[1]
Change in unrealized	(379)	[1]	(218)	[1]	(293)	[1]
Tax Effects [Member]
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(83)		(45)		(57)
Realized - impairments	9		18		22
Change in unrealized	(136)		(49)		(177)
Noncontrolling Interests [Member]
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(2)		(2)		(2)
Realized - impairments			1
Change in unrealized	(7)		(5)		(2)
Marketable Securities [Member]
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	151		81		104
Realized - impairments	(17)		(33)		(40)
Change in unrealized	$ 245		$ 87		$ 328

[1] Primarily adjustments to deferred policy acquisition costs and reserves related to annuities and long-term care business.