Fair Value (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Nonredeemable preferred stock
Fair value transfers due to changes in available market observable inputs
Transfer from level 1 to level 2	$ 21		$ 21
Transfer from level 2 to level 1	32		32
No. of securities transferred between Level 1 and Level 2	7		7
Level 3
Roll forward of Level 3 fair value measurements on a recurring basis for consolidated available-for-sale and trading securities
Beginning balance	88	75	71	78
Included in earnings	(1)	0	2	1
Included in other comprehensive income	(1)	(1)	0	0
Purchases	1	0	1	0
Sales	(4)	0	(8)	(5)
Transfers in and (out) of Level 3	0	0	17	0
Ending balance	83	74	83	74
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	0	0	0	0
Transfers in and (out) of Level 3	0	0	1	0
Ending balance	5	4	5	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	0	0	0	0
Transfers in and (out) of Level 3	0	0	1	0
Ending balance	5	4	5	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	0	0	0	0
Transfers in and (out) of Level 3	0	0	1	0
Ending balance	5	4	5	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	0	0	0	0
Transfers in and (out) of Level 3	0	0	0	0
Ending balance	4	4	4	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	83	71	67	74
Included in earnings	(1)	0	2	1
Included in other comprehensive income	(1)	(1)	0	0
Purchases	1	0	1	0
Sales	(4)	0	(8)	(5)
Transfers in and (out) of Level 3	0	0	16	0
Ending balance	78	70	78	70
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	69	58	55	62
Included in earnings	(1)	0	0	0
Included in other comprehensive income	(1)	(1)	0	0
Purchases	1	0	1	0
Sales	(4)	0	(8)	(5)
Transfers in and (out) of Level 3	0	0	16	0
Ending balance	64	57	64	57
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	0	0	2	1
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	14	13	14	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	63	50	50	55
Included in earnings	0	0	0	0
Included in other comprehensive income	(1)	0	0	0
Purchases	1	0	1	0
Sales	(4)	0	(8)	(5)
Transfers in and (out) of Level 3	0	0	16	0
Ending balance	59	50	59	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	5	4	4	4
Included in earnings	0	0	0	0
Included in other comprehensive income	(1)	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	26	11	12	11
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases	1	0	1	0
Sales	(4)	0	(4)	0
Transfers in and (out) of Level 3	0	0	14	0
Ending balance	23	11	23	11
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	0	0
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	(4)	0
Transfers in and (out) of Level 3	0	0	2	0
Ending balance	27	30	27	30
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	6	8	5	7
Included in earnings	(1)	0	0	0
Included in other comprehensive income	0	(1)	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	5	7	5	7
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	0	0	2	1
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	$ 14	$ 13	$ 14	$ 13