Invested Assets and Related Income (Details 5) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	$ 1,430	$ 4,189
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	65	122
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	676	862
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	79	125
Investment securities, Continuous unrealized loss position, Fair value, Total	2,106	5,051
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	144	247
Fixed Maturities [Member]
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	1,199	4,120
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	20	108
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	477	563
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	53	64
Investment securities, Continuous unrealized loss position, Fair value, Total	1,676	4,683
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	73	172
Equity securities [Member]
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	231	69
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	45	14
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	199	299
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	26	61
Investment securities, Continuous unrealized loss position, Fair value, Total	430	368
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	71	75
Tax Exempt [Member] | Fixed Maturities [Member]
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	81	2,498
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	1	79
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	240	284
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	36	43
Investment securities, Continuous unrealized loss position, Fair value, Total	321	2,782
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	37	122
Taxable [Member] | Fixed Maturities [Member]
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	1,118	1,622
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	19	29
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	237	279
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	17	21
Investment securities, Continuous unrealized loss position, Fair value, Total	1,355	1,901
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	36	50
U.S. Government and government agency and authority obligations [Member] | Taxable [Member] | Fixed Maturities [Member]
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	19	111
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	1	3
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	18	45
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	1	6
Investment securities, Continuous unrealized loss position, Fair value, Total	37	156
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	2	9
Corporate bonds [Member] | Taxable [Member] | Fixed Maturities [Member]
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	489	448
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	14	11
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	176	166
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	10	9
Investment securities, Continuous unrealized loss position, Fair value, Total	665	614
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	24	20
Foreign government and government agency obligations [Member] | Taxable [Member] | Fixed Maturities [Member]
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	499	1,016
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	1	13
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	21	27
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	1	1
Investment securities, Continuous unrealized loss position, Fair value, Total	520	1,043
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	2	14
Residential Mortgage-Backed Securities [Member] | Taxable [Member] | Fixed Maturities [Member]
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	77	9
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	2	1
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	22	41
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	5	5
Investment securities, Continuous unrealized loss position, Fair value, Total	99	50
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	7	6
Commercial Mortgage-Backed Securities [Member] | Taxable [Member] | Fixed Maturities [Member]
Fair value and gross unrealized depreciation of investments in an unrealized loss position [Abstract]
Investment securities, Continuous unrealized loss position, Less than twelve months, Fair value	34	38
Investment securities, Continuous unrealized loss position, Less than twelve months, Gross unrealized depreciation	1	1
Investment securities, Continuous unrealized loss position, Twelve months or longer, Fair value	0	0
Investment securities, Continuous unrealized loss position, Twelve months or longer, Gross unrealized depreciation	0	0
Investment securities, Continuous unrealized loss position, Fair value, Total	34	38
Investment securities, Continuous unrealized loss position, Gross unrealized depreciation, Total	$ 1	$ 1