Investments (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Realized capital gains and losses by asset type
Realized capital gains and losses	$ 327	$ 503	$ (827)
Fixed income securities
Realized capital gains and losses by asset type
Realized capital gains and losses	107	712	(366)
Equity securities
Realized capital gains and losses by asset type
Realized capital gains and losses	183	63	153
Mortgage loans
Realized capital gains and losses by asset type
Realized capital gains and losses	8	(27)	(71)
Limited partnership interests
Realized capital gains and losses by asset type
Realized capital gains and losses	13	159	57
Derivatives
Realized capital gains and losses by asset type
Realized capital gains and losses	23	(397)	(600)
Other
Realized capital gains and losses by asset type
Realized capital gains and losses	$ (7)	$ (7)