Investments (Details 3) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013 Holdings	Dec. 31, 2012 Holdings
Indemnity
Fair value
Less than 12 months	$ 84	$ 92
12 months or longer	3	6
Total	87	98
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	1
Total	0	1
No. of holdings	15	19
Indemnity | Investment grade
Fair value
Less than 12 months	45	55
12 months or longer	0	3
Total	45	58
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	9	12
Indemnity | Non-investment grade
Fair value
Less than 12 months	10	4
12 months or longer	0	0
Total	10	4
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	2	1
Indemnity | Fixed maturities
Fair value
Less than 12 months	55	59
12 months or longer	0	3
Total	55	62
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	11	13
Indemnity | Corporate debt securities
Fair value
Less than 12 months	55	59
12 months or longer	0	0
Total	55	59
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	11	12
Indemnity | Commercial mortgage-backed securities
Fair value
Less than 12 months		0
12 months or longer		3
Total		3
Unrealized losses
Less than 12 months		0
12 months or longer		0
Total		0
No. of holdings		1
Indemnity | Nonredeemable preferred stock
Fair value
Less than 12 months	3	7
12 months or longer	3	3
Total	6	10
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	1
Total	0	1
No. of holdings	2	4
Indemnity | Common stock
Fair value
Less than 12 months	26	26
12 months or longer	0	0
Total	26	26
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	2	2
Exchange
Fair value
Less than 12 months	920	694
12 months or longer	43	48
Total	963	742
Unrealized losses
Less than 12 months	13	7
12 months or longer	1	1
Total	14	8
No. of holdings	115	77
Exchange | Investment grade
Fair value
Less than 12 months	597	296
12 months or longer	22	24
Total	619	320
Unrealized losses
Less than 12 months	9	4
12 months or longer	0	0
Total	9	4
No. of holdings	105	53
Exchange | Non-investment grade
Fair value
Less than 12 months	3	20
12 months or longer	0	6
Total	3	26
Unrealized losses
Less than 12 months	0	1
12 months or longer	0	0
Total	0	1
No. of holdings	2	8
Exchange | Fixed maturities
Fair value
Less than 12 months	600	316
12 months or longer	22	30
Total	622	346
Unrealized losses
Less than 12 months	9	5
12 months or longer	0	0
Total	9	5
No. of holdings	107	61
Exchange | U.S. government & agencies
Fair value
Less than 12 months	84	80
12 months or longer	0	0
Total	84	80
Unrealized losses
Less than 12 months	1	1
12 months or longer	0	0
Total	1	1
No. of holdings	7	7
Exchange | States & political subdivisions
Fair value
Less than 12 months	72	23
12 months or longer	0	0
Total	72	23
Unrealized losses
Less than 12 months	1	0
12 months or longer	0	0
Total	1	0
No. of holdings	24	11
Exchange | Foreign government securities
Fair value
Less than 12 months	13
12 months or longer	0
Total	13
Unrealized losses
Less than 12 months	0
12 months or longer	0
Total	0
No. of holdings	2
Exchange | Corporate debt securities
Fair value
Less than 12 months	344	152
12 months or longer	1	9
Total	345	161
Unrealized losses
Less than 12 months	6	3
12 months or longer	0	0
Total	6	3
No. of holdings	58	31
Exchange | Residential mortgage-backed securities
Fair value
Less than 12 months	71	56
12 months or longer	0	0
Total	71	56
Unrealized losses
Less than 12 months	1	1
12 months or longer	0	0
Total	1	1
No. of holdings	12	9
Exchange | Commercial mortgage-backed 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 | Collateralized debt obligations
Fair value
Less than 12 months	0	0
12 months or longer	21	21
Total	21	21
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	1	1
Exchange | Other debt securities
Fair value
Less than 12 months	11	5
12 months or longer	0	0
Total	11	5
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	2	2
Exchange | Nonredeemable preferred stock
Fair value
Less than 12 months	8	64
12 months or longer	21	18
Total	29	82
Unrealized losses
Less than 12 months	0	0
12 months or longer	1	1
Total	1	1
No. of holdings	5	13
Exchange | Common stock
Fair value
Less than 12 months	312	314
12 months or longer	0	0
Total	312	314
Unrealized losses
Less than 12 months	4	2
12 months or longer	0	0
Total	$ 4	$ 2
No. of holdings	3	3