Investments (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011 security	Dec. 31, 2010 security
Indemnity
Fair value
Less than 12 months	$ 233	$ 98
12 months or longer	14	1
Total	247	99
Unrealized losses
Less than 12 months	1	2
12 months or longer	0	0
Total	1	2
No. of holdings	49	25
Indemnity | Investment grade
Fair value
Less than 12 months	229	95
12 months or longer	11	1
Total	240	96
Unrealized losses
Less than 12 months	1	2
12 months or longer	0	0
Total	1	2
No. of holdings	46	24
Indemnity | Non-investment grade
Fair value
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	0	0
Indemnity | Fixed maturities
Fair value
Less than 12 months	229	95
12 months or longer	11	1
Total	240	96
Unrealized losses
Less than 12 months	1	2
12 months or longer	0	0
Total	1	2
No. of holdings	46	24
Indemnity | U.S. government & agencies
Fair value
Less than 12 months		25
12 months or longer		0
Total		25
Unrealized losses
Less than 12 months		0
12 months or longer		0
Total		0
No. of holdings		1
Indemnity | States & political subdivisions
Fair value
Less than 12 months		39
12 months or longer		1
Total		40
Unrealized losses
Less than 12 months		2
12 months or longer		0
Total		2
No. of holdings		20
Indemnity | Corporate debt securities
Fair value
Less than 12 months	220	31
12 months or longer	0	0
Total	220	31
Unrealized losses
Less than 12 months	1	0
12 months or longer	0	0
Total	1	0
No. of holdings	41	3
Indemnity | Commercial mortgage-backed securities (CMBS)
Fair value
Less than 12 months	4
12 months or longer	9
Total	13
Unrealized losses
Less than 12 months	0
12 months or longer	0
Total	0
No. of holdings	3
Indemnity | Other debt securities
Fair value
Less than 12 months	5
12 months or longer	2
Total	7
Unrealized losses
Less than 12 months	0
12 months or longer	0
Total	0
No. of holdings	2
Indemnity | Nonredeemable preferred stock
Fair value
Less than 12 months	4	3
12 months or longer	3	0
Total	7	3
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	3	1
Exchange
Fair value
Less than 12 months	831	781
12 months or longer	122	260
Total	953	1,041
Unrealized losses
Less than 12 months	38	18
12 months or longer	11	19
Total	49	37
No. of holdings	151	191
Exchange | Investment grade
Fair value
Less than 12 months	625	703
12 months or longer	79	155
Total	704	858
Unrealized losses
Less than 12 months	26	16
12 months or longer	9	11
Total	35	27
No. of holdings	109	154
Exchange | Non-investment grade
Fair value
Less than 12 months	38	33
12 months or longer	9	46
Total	47	79
Unrealized losses
Less than 12 months	1	0
12 months or longer	1	3
Total	2	3
No. of holdings	15	22
Exchange | Fixed maturities
Fair value
Less than 12 months	663	736
12 months or longer	88	201
Total	751	937
Unrealized losses
Less than 12 months	27	16
12 months or longer	10	14
Total	37	30
No. of holdings	124	176
Exchange | U.S. government & agencies
Fair value
Less than 12 months		22
12 months or longer		0
Total		22
Unrealized losses
Less than 12 months		0
12 months or longer		0
Total		0
No. of holdings		3
Exchange | States & political subdivisions
Fair value
Less than 12 months	7	299
12 months or longer	6	5
Total	13	304
Unrealized losses
Less than 12 months	0	8
12 months or longer	1	1
Total	1	9
No. of holdings	3	59
Exchange | Foreign government securities
Fair value
Less than 12 months		10
12 months or longer		0
Total		10
Unrealized losses
Less than 12 months		0
12 months or longer		0
Total		0
No. of holdings		1
Exchange | Corporate debt securities
Fair value
Less than 12 months	635	398
12 months or longer	50	144
Total	685	542
Unrealized losses
Less than 12 months	27	8
12 months or longer	4	6
Total	31	14
No. of holdings	108	101
Exchange | Residential mortgage-backed securities (RMBS)
Fair value
Less than 12 months	7	6
12 months or longer	0	7
Total	7	13
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	1
Total	0	1
No. of holdings	4	4
Exchange | Commercial mortgage-backed securities (CMBS)
Fair value
Less than 12 months	5	0
12 months or longer	0	12
Total	5	12
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	1
Total	0	1
No. of holdings	1	2
Exchange | Collateralized debt obligations (CDO)
Fair value
Less than 12 months	0	1
12 months or longer	32	33
Total	32	34
Unrealized losses
Less than 12 months	0	0
12 months or longer	5	5
Total	5	5
No. of holdings	6	6
Exchange | Other debt securities
Fair value
Less than 12 months	9
12 months or longer	0
Total	9
Unrealized losses
Less than 12 months	0
12 months or longer	0
Total	0
No. of holdings	2
Exchange | Nonredeemable preferred stock
Fair value
Less than 12 months	168	45
12 months or longer	34	59
Total	202	104
Unrealized losses
Less than 12 months	11	2
12 months or longer	1	5
Total	$ 12	$ 7
No. of holdings	27	15