Invested Assets and Related Income (Details 7) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Sources of net investment income [Abstract]
Gross investment income	$ 1,644	$ 1,665	$ 1,649
Investment Expenses	39	35	39
Net investment income	1,605	1,630	1,610
Fixed Maturities [Member]
Sources of net investment income [Abstract]
Gross investment income	1,549	1,564	1,548
Equity securities [Member]
Sources of net investment income [Abstract]
Gross investment income	34	47	35
Short term investments [Member]
Sources of net investment income [Abstract]
Gross investment income	16	9	21
Other [Member]
Sources of net investment income [Abstract]
Gross investment income	$ 45	$ 45	$ 45