Investments (Details 3) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011 partnership holding	Dec. 31, 2010 partnership holding
Indemnity
Fair value
Less than 12 months	$ 230	$ 98
12 months or longer	5	1
Total	235	99
Unrealized losses
Less than 12 months	2	2
12 months or longer	0	0
Total	2	2
No. of holdings	45	25
Indemnity | Fixed maturities
Fair value
Less than 12 months	224	95
12 months or longer	2	1
Total	226	96
Unrealized losses
Less than 12 months	2	2
12 months or longer	0	0
Total	2	2
No. of holdings	41	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	0	39
12 months or longer	2	1
Total	2	40
Unrealized losses
Less than 12 months	0	2
12 months or longer	0	0
Total	0	2
No. of holdings	1	20
Indemnity | Corporate debt securities
Fair value
Less than 12 months	195	31
12 months or longer	0	0
Total	195	31
Unrealized losses
Less than 12 months	2	0
12 months or longer	0	0
Total	2	0
No. of holdings	34	3
Indemnity | 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
Indemnity | Commercial mortgage-backed securities (CMBS)
Fair value
Less than 12 months	20
12 months or longer	0
Total	20
Unrealized losses
Less than 12 months	0
12 months or longer	0
Total	0
No. of holdings	4
Indemnity | Nonredeemable preferred stock
Fair value
Less than 12 months	6	3
12 months or longer	3	0
Total	9	3
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	4	1
Indemnity | Investment grade
Fair value
Less than 12 months	224	95
12 months or longer	2	1
Total	226	96
Unrealized losses
Less than 12 months	2	2
12 months or longer	0	0
Total	2	2
No. of holdings	41	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
Exchange
Fair value
Less than 12 months	941	781
12 months or longer	131	260
Total	1,072	1,041
Unrealized losses
Less than 12 months	42	18
12 months or longer	11	19
Total	53	37
No. of holdings	175	191
Exchange | Fixed maturities
Fair value
Less than 12 months	785	736
12 months or longer	97	201
Total	882	937
Unrealized losses
Less than 12 months	30	16
12 months or longer	9	14
Total	39	30
No. of holdings	149	176
Exchange | U.S. government & agencies
Fair value
Less than 12 months	5	22
12 months or longer	0	0
Total	5	22
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	1	3
Exchange | States & political subdivisions
Fair value
Less than 12 months	9	299
12 months or longer	11	5
Total	20	304
Unrealized losses
Less than 12 months	0	8
12 months or longer	1	1
Total	1	9
No. of holdings	5	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	752	398
12 months or longer	54	144
Total	806	542
Unrealized losses
Less than 12 months	30	8
12 months or longer	3	6
Total	33	14
No. of holdings	130	101
Exchange | Other debt securities
Fair value
Less than 12 months	5
12 months or longer	0
Total	5
Unrealized losses
Less than 12 months	0
12 months or longer	0
Total	0
No. of holdings	1
Exchange | Residential mortgage-backed securities (RMBS)
Fair value
Less than 12 months	9	6
12 months or longer	0	7
Total	9	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	2	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 | Nonredeemable preferred stock
Fair value
Less than 12 months	156	45
12 months or longer	34	59
Total	190	104
Unrealized losses
Less than 12 months	12	2
12 months or longer	2	5
Total	14	7
No. of holdings	26	15
Exchange | Investment grade
Fair value
Less than 12 months	702	703
12 months or longer	90	155
Total	792	858
Unrealized losses
Less than 12 months	26	16
12 months or longer	8	11
Total	34	27
No. of holdings	127	154
Exchange | Non-investment grade
Fair value
Less than 12 months	83	33
12 months or longer	7	46
Total	90	79
Unrealized losses
Less than 12 months	4	0
12 months or longer	1	3
Total	$ 5	$ 3
No. of holdings	22	22