Fair Value (Details 2) (Level 3, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	$ 71	$ 78
Included in earnings	2	1
Included in other comprehensive income	2	1
Purchases	0	0
Sales	(4)	(5)
Transfers in and (out) of Level 3	17	0
Ending balance	88	75
Indemnity
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	1	0
Ending balance	5	4
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	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	1	0
Ending balance	5	4
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
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	0	0
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	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	1	0
Ending balance	5	4
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	0
Included in earnings	0
Included in other comprehensive income	0
Purchases	0
Sales	0
Transfers in and (out) of Level 3	1
Ending balance	1
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	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
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
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	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	67	74
Included in earnings	2	1
Included in other comprehensive income	2	1
Purchases	0	0
Sales	(4)	(5)
Transfers in and (out) of Level 3	16	0
Ending balance	83	71
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	55	62
Included in earnings	0	0
Included in other comprehensive income	2	1
Purchases	0	0
Sales	(4)	(5)
Transfers in and (out) of Level 3	16	0
Ending balance	69	58
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	12	12
Included in earnings	2	1
Included in other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Transfers in and (out) of Level 3	0	0
Ending balance	14	13
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	55
Included in earnings	0	0
Included in other comprehensive income	1	0
Purchases	0	0
Sales	(4)	(5)
Transfers in and (out) of Level 3	16	0
Ending balance	63	50
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	1	0
Purchases	0	0
Sales	0	0
Transfers in and (out) of Level 3	0	0
Ending balance	5	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	12	11
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	14	0
Ending balance	26	11
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	29	30
Included in earnings	0	0
Included in other comprehensive income	0	0
Purchases	0	0
Sales	(4)	0
Transfers in and (out) of Level 3	2	0
Ending balance	27	30
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	10
Included in earnings	0	0
Included in other comprehensive income	0	0
Purchases	0	0
Sales	0	(5)
Transfers in and (out) of Level 3	0	0
Ending balance	5	5
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	5	7
Included in earnings	0	0
Included in other comprehensive income	1	1
Purchases	0	0
Sales	0	0
Transfers in and (out) of Level 3	0	0
Ending balance	6	8
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	12	12
Included in earnings	2	1
Included in other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Transfers in and (out) of Level 3	0	0
Ending balance	$ 14	$ 13