Fair Value (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Level 3
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	$ 164,000,000	$ 206,000,000
Included in earnings	17,000,000	18,000,000
Included in other comprehensive income	(2,000,000)	0
Purchases	50,000,000	9,000,000
Sales	(63,000,000)	(61,000,000)
Transfers in and (out) of Level 3	28,000,000	(8,000,000)
Ending balance	194,000,000	164,000,000
Level 3 | Net realized investment gains (losses)
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Included in earnings	1,000,000	6,000,000
Level 3 | Equity in earnings of limited partnerships
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Included in earnings	16,000,000	12,000,000
Indemnity
Fair value transfers due to changes in available market observable inputs
Transfers from level 1 to level 2	0	0
Transfers from level 2 to level 1	0	1,000,000
Transfers from level 2 to level 3	0	0
Transfers from level 3 to level 2	4,000,000	0
Indemnity | Fixed maturities
Fair value transfers due to changes in available market observable inputs
No. of securities transferred between Level 3 and Level 2	2
Indemnity | Nonredeemable preferred stock
Fair value transfers due to changes in available market observable inputs
No. of securities transferred between Level 2 and Level 1		1
Indemnity | Level 3
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	20,000,000	23,000,000
Included in earnings	2,000,000	1,000,000
Included in other comprehensive income	0	0
Purchases	3,000,000	0
Sales	(13,000,000)	(4,000,000)
Transfers in and (out) of Level 3	(4,000,000)	0
Ending balance	8,000,000	20,000,000
Indemnity | Level 3 | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	2,000,000	4,000,000
Included in earnings	0	0
Included in other comprehensive income	0	0
Purchases	3,000,000	0
Sales	(1,000,000)	(2,000,000)
Transfers in and (out) of Level 3	(4,000,000)	0
Ending balance	0	2,000,000
Indemnity | Level 3 | Fixed maturities | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	2,000,000	4,000,000
Included in earnings	0	0
Included in other comprehensive income	0	0
Purchases	3,000,000	0
Sales	(1,000,000)	(2,000,000)
Transfers in and (out) of Level 3	(4,000,000)	0
Ending balance	0	2,000,000
Indemnity | Level 3 | Corporate debt securities | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	1,000,000	1,000,000
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	(1,000,000)	0
Ending balance	0	1,000,000
Indemnity | Level 3 | Commercial mortgage-backed securities | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	0
Included in earnings	0
Included in other comprehensive income	0
Purchases	3,000,000
Sales	0
Transfers in and (out) of Level 3	(3,000,000)
Ending balance	0
Indemnity | Level 3 | Collateralized debt obligations | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	1,000,000	3,000,000
Included in earnings	0	0
Included in other comprehensive income	0	0
Purchases	0	0
Sales	(1,000,000)	(2,000,000)
Transfers in and (out) of Level 3	0	0
Ending balance	0	1,000,000
Indemnity | Level 3 | Real estate | Limited partnerships
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	18,000,000	19,000,000
Included in earnings	2,000,000	1,000,000
Included in other comprehensive income	0	0
Purchases	0	0
Sales	(12,000,000)	(2,000,000)
Transfers in and (out) of Level 3	0	0
Ending balance	8,000,000	18,000,000
Exchange
Fair value transfers due to changes in available market observable inputs
Transfers from level 1 to level 2	36,000,000	6,000,000
Transfers from level 2 to level 1	25,000,000	51,000,000
Transfers from level 2 to level 3	56,000,000	39,000,000
Transfers from level 3 to level 2	24,000,000	47,000,000
Exchange | Fixed maturities
Fair value transfers due to changes in available market observable inputs
No. of securities transferred between Level 2 and Level 3	9	7
No. of securities transferred between Level 3 and Level 2	3	6
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	4	1
No. of securities transferred between Level 2 and Level 1	3	5
No. of securities transferred between Level 2 and Level 3	1	1
No. of securities transferred between Level 3 and Level 2	1
Exchange | Level 3
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	144,000,000	183,000,000
Included in earnings	15,000,000	17,000,000
Included in other comprehensive income	(2,000,000)	0
Purchases	47,000,000	9,000,000
Sales	(50,000,000)	(57,000,000)
Transfers in and (out) of Level 3	32,000,000	(8,000,000)
Ending balance	186,000,000	144,000,000
Exchange | Level 3 | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	31,000,000	59,000,000
Included in earnings	1,000,000	5,000,000
Included in other comprehensive income	(2,000,000)	0
Purchases	47,000,000	5,000,000
Sales	(9,000,000)	(30,000,000)
Transfers in and (out) of Level 3	32,000,000	(8,000,000)
Ending balance	100,000,000	31,000,000
Exchange | Level 3 | Trading securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	15,000,000	15,000,000
Included in earnings	0	1,000,000
Included in other comprehensive income	0	0
Purchases	0	4,000,000
Sales	0	(5,000,000)
Transfers in and (out) of Level 3	0	0
Ending balance	15,000,000	15,000,000
Exchange | Level 3 | Fixed maturities | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	31,000,000	59,000,000
Included in earnings	1,000,000	3,000,000
Included in other comprehensive income	(2,000,000)	1,000,000
Purchases	46,000,000	1,000,000
Sales	(9,000,000)	(20,000,000)
Transfers in and (out) of Level 3	32,000,000	(13,000,000)
Ending balance	99,000,000	31,000,000
Exchange | Level 3 | Corporate debt securities | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	26,000,000	43,000,000
Included in earnings	0	0
Included in other comprehensive income	(1,000,000)	0
Purchases	46,000,000	1,000,000
Sales	(6,000,000)	(3,000,000)
Transfers in and (out) of Level 3	22,000,000	(15,000,000)
Ending balance	87,000,000	26,000,000
Exchange | Level 3 | Commercial mortgage-backed securities | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance		0
Included in earnings		0
Included in other comprehensive income		0
Purchases		0
Sales		(1,000,000)
Transfers in and (out) of Level 3		1,000,000
Ending balance		0
Exchange | Level 3 | Collateralized debt obligations | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	5,000,000	16,000,000
Included in earnings	1,000,000	3,000,000
Included in other comprehensive income	(1,000,000)	1,000,000
Purchases	0	0
Sales	(3,000,000)	(16,000,000)
Transfers in and (out) of Level 3	(2,000,000)	1,000,000
Ending balance	0	5,000,000
Exchange | Level 3 | Other debt securities | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	0
Included in earnings	0
Included in other comprehensive income	0
Purchases	0
Sales	0
Transfers in and (out) of Level 3	12,000,000
Ending balance	12,000,000
Exchange | Level 3 | Nonredeemable preferred stock | Available-for-sale securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	0	0
Included in earnings	0	2,000,000
Included in other comprehensive income	0	(1,000,000)
Purchases	1,000,000	4,000,000
Sales	0	(10,000,000)
Transfers in and (out) of Level 3	0	5,000,000
Ending balance	1,000,000	0
Exchange | Level 3 | Common stock | Trading securities
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	15,000,000	15,000,000
Included in earnings	0	1,000,000
Included in other comprehensive income	0	0
Purchases	0	4,000,000
Sales	0	(5,000,000)
Transfers in and (out) of Level 3	0	0
Ending balance	15,000,000	15,000,000
Exchange | Level 3 | Real estate | Limited partnerships
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Beginning balance	98,000,000	109,000,000
Included in earnings	14,000,000	11,000,000
Included in other comprehensive income	0	0
Purchases	0	0
Sales	(41,000,000)	(22,000,000)
Transfers in and (out) of Level 3	0	0
Ending balance	71,000,000	98,000,000
Fair value measurements on a recurring basis | Indemnity | Real estate
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Ending balance	8,000,000	18,000,000
Fair value measurements on a recurring basis | Exchange | Real estate
Roll forward of Level 3 consolidated fair value measurements on a recurring basis
Ending balance	$ 71,000,000	$ 98,000,000