Investments (Details 3) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012 security	Dec. 31, 2011 security
Indemnity
Fair value
Less than 12 months	$ 58	$ 233
12 months or longer	16	14
Total	74	247
Unrealized losses
Less than 12 months	0	1
12 months or longer	0	0
Total	0	1
No. of holdings	16	49
Indemnity | Investment grade
Fair value
Less than 12 months	58	229
12 months or longer	13	11
Total	71	240
Unrealized losses
Less than 12 months	0	1
12 months or longer	0	0
Total	0	1
No. of holdings	15	46
Indemnity | Non-investment grade
Fair value
Less than 12 months		0
12 months or longer		0
Total		0
Unrealized losses
Less than 12 months		0
12 months or longer		0
Total		0
No. of holdings		0
Indemnity | Fixed maturities
Fair value
Less than 12 months	58	229
12 months or longer	13	11
Total	71	240
Unrealized losses
Less than 12 months	0	1
12 months or longer	0	0
Total	0	1
No. of holdings	15	46
Indemnity | Corporate debt securities
Fair value
Less than 12 months	50	220
12 months or longer	6	0
Total	56	220
Unrealized losses
Less than 12 months	0	1
12 months or longer	0	0
Total	0	1
No. of holdings	10	41
Indemnity | Commercial mortgage-backed securities (CMBS)
Fair value
Less than 12 months	4	4
12 months or longer	6	9
Total	10	13
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	3	3
Indemnity | Other debt securities
Fair value
Less than 12 months	4	5
12 months or longer	1	2
Total	5	7
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	2	2
Indemnity | Nonredeemable preferred stock
Fair value
Less than 12 months	0	4
12 months or longer	3	3
Total	3	7
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	1	3
Exchange
Fair value
Less than 12 months	465	831
12 months or longer	107	122
Total	572	953
Unrealized losses
Less than 12 months	9	38
12 months or longer	7	11
Total	16	49
No. of holdings	91	151
Exchange | Investment grade
Fair value
Less than 12 months	321	625
12 months or longer	73	79
Total	394	704
Unrealized losses
Less than 12 months	5	26
12 months or longer	4	9
Total	9	35
No. of holdings	64	109
Exchange | Non-investment grade
Fair value
Less than 12 months	52	38
12 months or longer	8	9
Total	60	47
Unrealized losses
Less than 12 months	1	1
12 months or longer	1	1
Total	2	2
No. of holdings	11	15
Exchange | Fixed maturities
Fair value
Less than 12 months	373	663
12 months or longer	81	88
Total	454	751
Unrealized losses
Less than 12 months	6	27
12 months or longer	5	10
Total	11	37
No. of holdings	75	124
Exchange | States & political subdivisions
Fair value
Less than 12 months	13	7
12 months or longer	9	6
Total	22	13
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	1
Total	0	1
No. of holdings	4	3
Exchange | Corporate debt securities
Fair value
Less than 12 months	342	635
12 months or longer	39	50
Total	381	685
Unrealized losses
Less than 12 months	6	27
12 months or longer	3	4
Total	9	31
No. of holdings	59	108
Exchange | Residential mortgage-backed securities (RMBS)
Fair value
Less than 12 months	3	7
12 months or longer	0	0
Total	3	7
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	2	4
Exchange | Commercial mortgage-backed securities (CMBS)
Fair value
Less than 12 months	10	5
12 months or longer	0	0
Total	10	5
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	4	1
Exchange | Collateralized debt obligations (CDO)
Fair value
Less than 12 months	0	0
12 months or longer	33	32
Total	33	32
Unrealized losses
Less than 12 months	0	0
12 months or longer	2	5
Total	2	5
No. of holdings	5	6
Exchange | Other debt securities
Fair value
Less than 12 months	5	9
12 months or longer	0	0
Total	5	9
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	1	2
Exchange | Nonredeemable preferred stock
Fair value
Less than 12 months	92	168
12 months or longer	26	34
Total	118	202
Unrealized losses
Less than 12 months	3	11
12 months or longer	2	1
Total	$ 5	$ 12
No. of holdings	16	27