Investments (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012 Holdings	Dec. 31, 2011 Holdings
Indemnity
Fair value
Less than 12 months	$ 92	$ 233
12 months or longer	6	14
Total	98	247
Unrealized losses
Less than 12 months	0	1
12 months or longer	1	0
Total	1	1
No. of holdings	19	49
Indemnity | Investment grade
Fair value
Less than 12 months	55	229
12 months or longer	3	11
Total	58	240
Unrealized losses
Less than 12 months	0	1
12 months or longer	0	0
Total	0	1
No. of holdings	12	46
Indemnity | Non-investment grade
Fair value
Less than 12 months	4	0
12 months or longer	0	0
Total	4	0
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	1	0
Indemnity | Fixed maturities
Fair value
Less than 12 months	59	229
12 months or longer	3	11
Total	62	240
Unrealized losses
Less than 12 months	0	1
12 months or longer	0	0
Total	0	1
No. of holdings	13	46
Indemnity | Corporate debt securities
Fair value
Less than 12 months	59	220
12 months or longer	0	0
Total	59	220
Unrealized losses
Less than 12 months	0	1
12 months or longer	0	0
Total	0	1
No. of holdings	12	41
Indemnity | Commercial mortgage-backed securities (CMBS)
Fair value
Less than 12 months	0	4
12 months or longer	3	9
Total	3	13
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
No. of holdings	1	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	7	4
12 months or longer	3	3
Total	10	7
Unrealized losses
Less than 12 months	0	0
12 months or longer	1	0
Total	1	0
No. of holdings	4	3
Indemnity | Common stock
Fair value
Less than 12 months	26
12 months or longer	0
Total	26
Unrealized losses
Less than 12 months	0
12 months or longer	0
Total	0
No. of holdings	2
Exchange
Fair value
Less than 12 months	694	831
12 months or longer	48	122
Total	742	953
Unrealized losses
Less than 12 months	7	38
12 months or longer	1	11
Total	8	49
No. of holdings	77	151
Exchange | Investment grade
Fair value
Less than 12 months	296	625
12 months or longer	24	79
Total	320	704
Unrealized losses
Less than 12 months	4	26
12 months or longer	0	9
Total	4	35
No. of holdings	53	109
Exchange | Non-investment grade
Fair value
Less than 12 months	20	38
12 months or longer	6	9
Total	26	47
Unrealized losses
Less than 12 months	1	1
12 months or longer	0	1
Total	1	2
No. of holdings	8	15
Exchange | Fixed maturities
Fair value
Less than 12 months	316	663
12 months or longer	30	88
Total	346	751
Unrealized losses
Less than 12 months	5	27
12 months or longer	0	10
Total	5	37
No. of holdings	61	124
Exchange | Corporate debt securities
Fair value
Less than 12 months	152	635
12 months or longer	9	50
Total	161	685
Unrealized losses
Less than 12 months	3	27
12 months or longer	0	4
Total	3	31
No. of holdings	31	108
Exchange | U.S. government & agencies
Fair value
Less than 12 months	80
12 months or longer	0
Total	80
Unrealized losses
Less than 12 months	1
12 months or longer	0
Total	1
No. of holdings	7
Exchange | Commercial mortgage-backed securities (CMBS)
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 | States & political subdivisions
Fair value
Less than 12 months	23	7
12 months or longer	0	6
Total	23	13
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	1
Total	0	1
No. of holdings	11	3
Exchange | Residential mortgage-backed securities (RMBS)
Fair value
Less than 12 months	56	7
12 months or longer	0	0
Total	56	7
Unrealized losses
Less than 12 months	1	0
12 months or longer	0	0
Total	1	0
No. of holdings	9	4
Exchange | Collateralized debt obligations (CDO)
Fair value
Less than 12 months	0	0
12 months or longer	21	32
Total	21	32
Unrealized losses
Less than 12 months	0	0
12 months or longer	0	5
Total	0	5
No. of holdings	1	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	2	2
Exchange | Nonredeemable preferred stock
Fair value
Less than 12 months	64	168
12 months or longer	18	34
Total	82	202
Unrealized losses
Less than 12 months	0	11
12 months or longer	1	1
Total	1	12
No. of holdings	13	27
Exchange | Common stock
Fair value
Less than 12 months	314
12 months or longer	0
Total	314
Unrealized losses
Less than 12 months	2
12 months or longer	0
Total	$ 2
No. of holdings	3