Investments (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012 security	Mar. 31, 2011	Dec. 31, 2011
Investments [Abstract]
Net unrealized appreciation (depreciation) included in OCI	$ 68,000,000	$ 18,000,000
Net unrealized depreciation included in AOCI	87,000,000		155,000,000
Percentage of mortgage-backed securities represented by investments in US government agency bonds	85.00%		84.00%
Credit losses recognized in net income for corporate securities	3,000,000	0
Credit losses in net income relating to mortgage-backed securities	3,000,000	1,000,000
Number of fixed maturities in an unrealized loss position	2,900
Total number of fixed maturities	22,584
Largest single unrealized loss in the fixed maturities	7,000,000
Number of equity securities in an unrealized loss position	62
Total number of equity securities	174
Largest single unrealized loss in the equity securities	8,000,000
Restricted assets in fixed maturities and short-term investments	15,600,000,000		14,900,000,000
Restricted assets in cash	$ 291,000,000		$ 179,000,000