Fair Value (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Level 3
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	$ 198	$ 208	$ 206	$ 190
Included in earnings	6	2	14	13
Included in other comprehensive income	(3)	2	(1)	5
Purchases	4	0	9	1
Sales	(24)	(7)	(50)	(17)
Transfers in and (out) of Level 3	(11)	33	(8)	46
Ending balance	170	238	170	238
Level 3 | Net realized investment gains losses
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Included in earnings	3	(1)	4	3
Level 3 | Equity in earnings of limited partnerships
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Included in earnings	3	3	10	10
Indemnity
Fair value transfers due to changes in available market observable inputs
Transfers from level 1 to level 2	0	2	0	3
Transfers from level 2 to level 1	0	1	1	1
Transfers from level 2 to level 3	0	0	0	1
Transfers from level 3 to level 2	0	0	0	0
Indemnity | Fixed maturities
Fair value transfers due to changes in available market observable inputs
No. of securities transferred between Level 2 and Level 3				1
Indemnity | Nonredeemable preferred stock
Fair value transfers due to changes in available market observable inputs
No. of securities transferred between Level 1 and Level 2		1		2
No. of securities transferred between Level 2 and Level 1		1	1	1
Indemnity | Level 3
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	22	23	23	21
Included in earnings	0	0	1	1
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	(1)	(1)	(3)	(1)
Transfers in and (out) of Level 3	0	0	0	1
Ending balance	21	22	21	22
Indemnity | Level 3 | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	2	5	4	4
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	(1)	(2)	(1)
Transfers in and (out) of Level 3	0	0	0	1
Ending balance	2	4	2	4
Indemnity | Level 3 | Fixed maturities | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	2	5	4	4
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	(1)	(2)	(1)
Transfers in and (out) of Level 3	0	0	0	1
Ending balance	2	4	2	4
Indemnity | Level 3 | Corporate debt securities | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	1	1	1	0
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Transfers in and (out) of Level 3	0	0	0	1
Ending balance	1	1	1	1
Indemnity | Level 3 | Collateralized debt obligations | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	1	4	3	4
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	(1)	(2)	(1)
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	1	3	1	3
Indemnity | Level 3 | Real estate | Limited partnerships
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	20	18	19	17
Included in earnings	0	0	1	1
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	(1)	0	(1)	0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	19	18	19	18
Exchange
Fair value transfers due to changes in available market observable inputs
Transfers from level 1 to level 2	0	42	6	56
Transfers from level 2 to level 1	0	35	51	53
Transfers from level 2 to level 3	0	34	39	46
Transfers from level 3 to level 2	11	1	47	1
Exchange | Fixed maturities
Fair value transfers due to changes in available market observable inputs
No. of securities transferred between Level 2 and Level 3		4	7	8
No. of securities transferred between Level 3 and Level 2	2	1	6	1
Exchange | Nonredeemable preferred stock
Fair value transfers due to changes in available market observable inputs
No. of securities transferred between Level 1 and Level 2		3	1	6
No. of securities transferred between Level 2 and Level 1		5	5	6
No. of securities transferred between Level 2 and Level 3			1
Exchange | Level 3
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	176	185	183	169
Included in earnings	6	2	13	12
Included in other comprehensive income	(3)	2	(1)	5
Purchases	4	0	9	1
Sales	(23)	(6)	(47)	(16)
Transfers in and (out) of Level 3	(11)	33	(8)	45
Ending balance	149	216	149	216
Exchange | Level 3 | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	56	64	59	55
Included in earnings	0	0	4	1
Included in other comprehensive income	(3)	2	(1)	5
Purchases	0	0	5	1
Sales	(7)	(4)	(24)	(12)
Transfers in and (out) of Level 3	(11)	33	(8)	45
Ending balance	35	95	35	95
Exchange | Level 3 | Trading securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	7	14	15	12
Included in earnings	3	(1)	0	2
Included in other comprehensive income	0	0	0	0
Purchases	4	0	4	0
Sales	0	0	(5)	(1)
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	14	13	14	13
Exchange | Level 3 | Fixed maturities | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	49	59	59	50
Included in earnings	0	0	2	1
Included in other comprehensive income	0	1	0	4
Purchases	0	0	1	1
Sales	(3)	(4)	(14)	(12)
Transfers in and (out) of Level 3	(11)	33	(13)	45
Ending balance	35	89	35	89
Exchange | Level 3 | States & political subdivisions | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance		4		4
Included in earnings		0		0
Included in other comprehensive income		0		0
Purchases		0		0
Sales		0		0
Transfers in and (out) of Level 3		0		0
Ending balance		4		4
Exchange | Level 3 | Corporate debt securities | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	33	23	43	12
Included in earnings	0	0	0	0
Included in other comprehensive income	0	1	0	1
Purchases	0	0	1	1
Sales	0	0	(3)	(5)
Transfers in and (out) of Level 3	(7)	10	(15)	25
Ending balance	26	34	26	34
Exchange | Level 3 | Commercial mortgage-backed securities | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	4		0
Included in earnings	0		0
Included in other comprehensive income	0		0
Purchases	0		0
Sales	0		(1)
Transfers in and (out) of Level 3	(4)		1
Ending balance	0		0
Exchange | Level 3 | Collateralized debt obligations | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	12	27	16	29
Included in earnings	0	0	2	1
Included in other comprehensive income	0	0	0	3
Purchases	0	0	0	0
Sales	(3)	(4)	(10)	(7)
Transfers in and (out) of Level 3	0	23	1	20
Ending balance	9	46	9	46
Exchange | Level 3 | Other debt securities | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance		5		5
Included in earnings		0		0
Included in other comprehensive income		0		0
Purchases		0		0
Sales		0		0
Transfers in and (out) of Level 3		0		0
Ending balance		5		5
Exchange | Level 3 | Nonredeemable preferred stock | Available-for-sale securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	7	5	0	5
Included in earnings	0	0	2	0
Included in other comprehensive income	(3)	1	(1)	1
Purchases	0	0	4	0
Sales	(4)	0	(10)	0
Transfers in and (out) of Level 3	0	0	5	0
Ending balance	0	6	0	6
Exchange | Level 3 | Common stock | Trading securities
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	7	14	15	12
Included in earnings	3	(1)	0	2
Included in other comprehensive income	0	0	0	0
Purchases	4	0	4	0
Sales	0	0	(5)	(1)
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	14	13	14	13
Exchange | Level 3 | Real estate | Limited partnerships
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Beginning balance	113	107	109	102
Included in earnings	3	3	9	9
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	(16)	(2)	(18)	(3)
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	100	108	100	108
Fair value measurements on a recurring basis
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Ending balance	170		170
Fair value measurements on a recurring basis | Indemnity
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Ending balance	21		21
Fair value measurements on a recurring basis | Indemnity | Real estate
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Ending balance	19		19
Fair value measurements on a recurring basis | Exchange
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Ending balance	149		149
Fair value measurements on a recurring basis | Exchange | Real estate
Roll forward of consolidated level 3 fair value measurements on a recurring basis
Ending balance	$ 100		$ 100