Investments (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Net Investment Income:
Investment income, before expense	$ 1,031	$ 1,060
Investment expense	(48)	(49)
Net investment income	983	1,011
Fixed income securities
Net Investment Income:
Investment income, before expense	762	806
Equity securities
Net Investment Income:
Investment income, before expense	25	21
Mortgage loans
Net Investment Income:
Investment income, before expense	98	93
Limited partnership interests
Net Investment Income:
Investment income, before expense	107	109
Short-term investments
Net Investment Income:
Investment income, before expense	2	1
Other
Net Investment Income:
Investment income, before expense	$ 37	$ 30