Fair Value (Details 2) (Level 3, USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	$ 74	$ 92	$ 78	$ 95
Included in earnings	0	1	2	4
Included in other comprehensive income	(2)	0	(2)	5
Purchases, sales and adjustments		1		1
Purchases	1		1
Sales	0		(6)
Transfers in and (out) of Level 3	0	(11)	0	(22)
Ending balance	73	83	73	83
Unrealized gains included in earnings on Level 3 securities		1	1	2
Indemnity
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	4	11	4	11
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases, sales and adjustments		1		1
Purchases	0		0
Sales	0		0
Transfers in and (out) of Level 3	0	(1)	0	(1)
Ending balance	4	11	4	11
Indemnity | 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	4	10	4	10
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases, sales and adjustments		0		0
Purchases	0		0
Sales	0		0
Transfers in and (out) of Level 3	0	(1)	0	(1)
Ending balance	4	9	4	9
Indemnity | 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		2		2
Included in earnings		0		0
Included in other comprehensive income		0		0
Purchases, sales and adjustments		0		0
Transfers in and (out) of Level 3		0		0
Ending balance		2		2
Indemnity | 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	8	4	8
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases, sales and adjustments		0		0
Purchases	0		0
Sales	0		0
Transfers in and (out) of Level 3	0	(1)	0	(1)
Ending balance	4	7	4	7
Indemnity | 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		1		1
Included in earnings		0		0
Included in other comprehensive income		0		0
Purchases, sales and adjustments		1		1
Transfers in and (out) of Level 3		0		0
Ending balance		2		2
Indemnity | 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, sales and adjustments		0		0
Purchases	0		0
Sales	0		0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	0	0	0	0
Indemnity | 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	11	4	11
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases, sales and adjustments		1		1
Purchases	0		0
Sales	0		0
Transfers in and (out) of Level 3	0	(1)	0	(1)
Ending balance	4	11	4	11
Indemnity | 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, sales and adjustments		0		0
Purchases	0		0
Sales	0		0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	0	0	0	0
Exchange
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	70	81	74	84
Included in earnings	0	1	2	4
Included in other comprehensive income	(2)	0	(2)	5
Purchases, sales and adjustments		0		0
Purchases	1		1
Sales	0		(6)
Transfers in and (out) of Level 3	0	(10)	0	(21)
Ending balance	69	72	69	72
Exchange | 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	50	67	55	71
Included in earnings	0	0	1	2
Included in other comprehensive income	(1)	0	(1)	4
Purchases, sales and adjustments		(1)		0
Purchases	1		1
Sales	0		(6)
Transfers in and (out) of Level 3	0	(10)	0	(21)
Ending balance	50	56	50	56
Exchange | 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
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 | 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	11	9	11	17
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases, sales and adjustments		0		0
Purchases	1		1
Sales	0		0
Transfers in and (out) of Level 3	0	0	0	(8)
Ending balance	12	9	12	9
Exchange | 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	10	5
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases, sales and adjustments		0		0
Purchases	0		0
Sales	0		(5)
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	5	5	5	5
Exchange | 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	30	53	30	49
Included in earnings	0	0	1	2
Included in other comprehensive income	(1)	0	(1)	4
Purchases, sales and adjustments		(1)		0
Purchases	0		0
Sales	0		(1)
Transfers in and (out) of Level 3	0	(10)	0	(13)
Ending balance	29	42	29	42
Exchange | 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	7	4	7	4
Included in earnings	0	0	0	0
Included in other comprehensive income	(1)	0	(1)	1
Purchases, sales and adjustments		1		0
Purchases	0		0
Sales	0		0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	6	5	6	5
Exchange | 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	13	10	12	9
Included in earnings	0	1	1	2
Included in other comprehensive income	0	0	0	0
Purchases, sales and adjustments		0		0
Purchases	0		0
Sales	0		0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	13	11	13	11
Exchange | 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	57	71	62	75
Included in earnings	0	0	1	2
Included in other comprehensive income	(2)	0	(2)	5
Purchases, sales and adjustments		0		0
Purchases	1		1
Sales	0		(6)
Transfers in and (out) of Level 3	0	(10)	0	(21)
Ending balance	56	61	56	61
Exchange | Trading securities
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	13	10	12	9
Included in earnings	0	1	1	2
Included in other comprehensive income	0	0	0	0
Purchases, sales and adjustments		0		0
Purchases	0		0
Sales	0		0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	$ 13	$ 11	$ 13	$ 11