Investments (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Realized capital gains and losses by asset type
Realized capital gains and losses	$ 19	$ (22)
Fixed income securities
Realized capital gains and losses by asset type
Realized capital gains and losses	(18)	(50)
Mortgage loans
Realized capital gains and losses by asset type
Realized capital gains and losses	31	(1)
Equity securities
Realized capital gains and losses by asset type
Realized capital gains and losses	1
Limited partnership interests
Realized capital gains and losses by asset type
Realized capital gains and losses		(1)
Derivatives
Realized capital gains and losses by asset type
Realized capital gains and losses	7	22
Other
Realized capital gains and losses by asset type
Realized capital gains and losses	$ (2)	$ 8