Investments (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Investment Income:
Investment income, before expense	$ 4,221	$ 4,154	$ 4,279
Investment expense	(211)	(183)	(177)
Net investment income	4,010	3,971	4,102
Fixed income securities
Net Investment Income:
Investment income, before expense	3,234	3,484	3,737
Equity securities
Net Investment Income:
Investment income, before expense	127	122	90
Mortgage loans
Net Investment Income:
Investment income, before expense	374	359	385
Limited partnership interests
Net Investment Income:
Investment income, before expense	348	88	40
Short-term investments
Net Investment Income:
Investment income, before expense	6	6	8
Other
Net Investment Income:
Investment income, before expense	$ 132	$ 95	$ 19