Fair Value (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Fair value transfers due to changes in available market observable inputs
Transfers from level 1 to level 2	$ 44		$ 59
Transfers from level 2 to level 1	36		54
Fixed maturities
Fair value transfers due to changes in available market observable inputs
No. of securities transferred between Level 1 and Level 2	1
Nonredeemable preferred stock
Fair value transfers due to changes in available market observable inputs
No. of securities transferred between Level 1 and Level 2	7		12
Level 3
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	83	74	71	78
Included in earnings	(1)	0	3	2
Included in other comprehensive income	2	(2)	5	(2)
Purchases	0	1	1	1
Sales	(5)	0	(14)	(6)
Transfers in and (out) of Level 3	33	0	46	0
Ending balance	112	73	112	73
Indemnity | Level 3
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	5	4	4	4
Included in earnings	0	0	0	0
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	1	0
Ending balance	4	4	4	4
Indemnity | Level 3 | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	5	4	4	4
Included in earnings	0	0	0	0
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	1	0
Ending balance	4	4	4	4
Indemnity | Level 3 | Trading securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	0	0	0	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	0
Ending balance	0	0	0	0
Indemnity | Level 3 | Fixed maturities | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	5	4	4	4
Included in earnings	0	0	0	0
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	1	0
Ending balance	4	4	4	4
Indemnity | Level 3 | Corporate debt securities | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	1		0
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		1
Ending balance	1		1
Indemnity | Level 3 | Collateralized debt obligations (CDO) | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	4	4	4	4
Included in earnings	0	0	0	0
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	3	4	3	4
Indemnity | Level 3 | Common stock | Trading securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	0	0	0	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	0
Ending balance	0	0	0	0
Exchange | Level 3
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	78	70	67	74
Included in earnings	(1)	0	3	2
Included in other comprehensive income	2	(2)	5	(2)
Purchases	0	1	1	1
Sales	(4)	0	(13)	(6)
Transfers in and (out) of Level 3	33	0	45	0
Ending balance	108	69	108	69
Exchange | Level 3 | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	64	57	55	62
Included in earnings	0	0	1	1
Included in other comprehensive income	2	(2)	5	(2)
Purchases	0	1	1	1
Sales	(4)	0	(12)	(6)
Transfers in and (out) of Level 3	33	0	45	0
Ending balance	95	56	95	56
Exchange | Level 3 | Trading securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	14	13	12	12
Included in earnings	(1)	0	2	1
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	(1)	0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	13	13	13	13
Exchange | Level 3 | Fixed maturities | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	59	50	50	55
Included in earnings	0	0	1	1
Included in other comprehensive income	1	(1)	4	(1)
Purchases	0	1	1	1
Sales	(4)	0	(12)	(6)
Transfers in and (out) of Level 3	33	0	45	0
Ending balance	89	50	89	50
Exchange | Level 3 | States & political subdivisions | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	4	4	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	0	0	0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	4	4	4	4
Exchange | Level 3 | Corporate debt securities | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	23	11	12	11
Included in earnings	0	0	0	0
Included in other comprehensive income	1	0	1	0
Purchases	0	1	1	1
Sales	0	0	(5)	0
Transfers in and (out) of Level 3	10	0	25	0
Ending balance	34	12	34	12
Exchange | Level 3 | Collateralized debt obligations (CDO) | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	27	30	29	30
Included in earnings	0	0	1	1
Included in other comprehensive income	0	(1)	3	(1)
Purchases	0	0	0	0
Sales	(4)	0	(7)	(1)
Transfers in and (out) of Level 3	23	0	20	0
Ending balance	46	29	46	29
Exchange | Level 3 | Other debt securities | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	5	5	5	10
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	(5)
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	5	5	5	5
Exchange | Level 3 | Nonredeemable preferred stock | Available-for-sale securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	5	7	5	7
Included in earnings	0	0	0	0
Included in other comprehensive income	1	(1)	1	(1)
Purchases	0	0	0	0
Sales	0	0	0	0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	6	6	6	6
Exchange | Level 3 | Common stock | Trading securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	14	13	12	12
Included in earnings	(1)	0	2	1
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	(1)	0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	$ 13	$ 13	$ 13	$ 13