Investments (Details 4) (USD $)	Sep. 30, 2011 security segment entity agreement market subsidiary company policy D transaction counterparty	Dec. 31, 2010 entity security policy
Less than 12 months
Fair value	$ 499,000,000	$ 2,828,200,000
Unrealized loss	(82,500,000)	(116,900,000)
12 months or more
Fair Value	84,700,000	63,100,000
Unrealized loss	(27,000,000)	(15,400,000)
Total
Fair value	583,700,000	2,891,300,000
Unrealized loss	(109,500,000)	(132,300,000)
Number of securities
Less than 12 months (in securities)	81	405
12 months or more (in securities)	23	18
Total (in securities)	104	423
Number of securities with OTTI
Less than 12 months (in securities)	6	10
12 months or more (in securities)	3	3
Total (in securities)	9	13
Number of securities with unrealized losses greater than 10% of book value for 12 months or more	6
Threshold for measuring unrealized losses for securities as a percent of book value	10.00%
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more	24,800,000
U.S. government and agencies
Less than 12 months
Fair value	3,800,000	20,500,000
Unrealized loss	(100,000)	(400,000)
Total
Fair value	3,800,000	20,500,000
Unrealized loss	(100,000)	(400,000)
Obligations of state and political subdivisions
Less than 12 months
Fair value	45,300,000	1,694,500,000
Unrealized loss	(900,000)	(58,900,000)
12 months or more
Fair Value	49,700,000	23,500,000
Unrealized loss	(900,000)	(3,100,000)
Total
Fair value	95,000,000	1,718,000,000
Unrealized loss	(1,800,000)	(62,000,000)
Corporate securities
Less than 12 months
Fair value	153,100,000	403,600,000
Unrealized loss	(2,300,000)	(12,800,000)
Total
Fair value	153,100,000	403,600,000
Unrealized loss	(2,300,000)	(12,800,000)
RMBS
Less than 12 months
Fair value	121,400,000	143,400,000
Unrealized loss	(54,600,000)	(32,100,000)
12 months or more
Fair Value	32,800,000	37,300,000
Unrealized loss	(26,000,000)	(12,200,000)
Total
Fair value	154,200,000	180,700,000
Unrealized loss	(80,600,000)	(44,300,000)
CMBS
Less than 12 months
Fair value	9,900,000	92,600,000
Unrealized loss	0	(1,400,000)
Total
Fair value	9,900,000	92,600,000
Unrealized loss	0	(1,400,000)
Asset-backed securities
Less than 12 months
Fair value	22,500,000	228,300,000
Unrealized loss	(19,300,000)	(5,100,000)
12 months or more
Fair Value	2,200,000	2,300,000
Unrealized loss	(100,000)	(100,000)
Total
Fair value	24,700,000	230,600,000
Unrealized loss	(19,400,000)	(5,200,000)
Foreign government securities
Less than 12 months
Fair value	143,000,000	245,300,000
Unrealized loss	(5,300,000)	(6,200,000)
Total
Fair value	143,000,000	245,300,000
Unrealized loss	$ (5,300,000)	$ (6,200,000)