8. Investing Activities (Details 3) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
U.S. government and agency	$ 932.7
State and political subdivision	344.5
Foreign government	214.6
Corporate	7,406.4
Commercial mortgage-backed ("CMBS")	7.9
Residential mortgage-backed ("RMBS")	1,881.6
CDO/CLO	216.5
Other asset-backed	467.1
Less than 12 months | Fair Value
U.S. government and agency	0.9
State and political subdivision	12.8	26.1
Foreign government		25.6
Corporate	152.5	367.0
Commercial mortgage-backed ("CMBS")	10.7	132.4
Residential mortgage-backed ("RMBS")	37.7	178.1
CDO/CLO	22.9	15.4
Other asset-backed	21.1	101.3
Debt securities	258.6	845.9
Equity securities	1.1	12.1
Total temporarily impaired securities	259.7	858.0
Amounts inside the closed block	106.6	308.5
Amounts outside the closed block	153.1	549.5
Amounts outside the closed block that are below investment grade	46.6	68.8
Less than 12 months | Unrealized Losses
U.S. government and agency		(2.4)
State and political subdivision	(0.8)	(0.1)
Foreign government		(1.7)
Corporate	(7.5)	(29.4)
Commercial mortgage-backed ("CMBS")		(4.1)
Residential mortgage-backed ("RMBS")	(0.3)	(7.8)
CDO/CLO	(2.9)	(0.8)
Other asset-backed	(1.3)	(2.1)
Debt securities	(12.8)	(48.4)
Equity securities	(0.2)	(7.0)
Total temporarily impaired securities	(13.0)	(55.4)
Amounts inside the closed block	(5.1)	(23.6)
Amounts outside the closed block	(7.9)	(31.8)
Amounts outside the closed block that are below investment grade	(4.2)	(13.9)
Number of securities	70	255
Greater than 12 months | Fair Value
U.S. government and agency	35.5	(5.4)
State and political subdivision	6.7	(2.8)
Foreign government
Corporate	362.3	(142.0)
Commercial mortgage-backed ("CMBS")	51.3	(15.9)
Residential mortgage-backed ("RMBS")	274.7	(62.8)
CDO/CLO	145.1	(53.1)
Other asset-backed	36.8	(14.2)
Debt securities	912.4	(296.2)
Equity securities	6.3	(0.8)
Total temporarily impaired securities	918.7	(297.0)
Amounts inside the closed block	394.6	(106.6)
Amounts outside the closed block	524.1	(190.4)
Amounts outside the closed block that are below investment grade	177.8	(125.2)
Number of securities		304
Greater than 12 months | Unrealized Losses
U.S. government and agency	(5.4)	41.2
State and political subdivision	(2.3)	6.2
Foreign government
Corporate	(79.4)	501.2
Commercial mortgage-backed ("CMBS")	(8.3)	52.1
Residential mortgage-backed ("RMBS")	(29.0)	392.4
CDO/CLO	(27.5)	167.6
Other asset-backed	(11.7)	57.8
Debt securities	(163.6)	1,218.5
Equity securities	(6.5)	0.4
Total temporarily impaired securities	(170.1)	1,218.9
Amounts inside the closed block	(50.7)	552.7
Amounts outside the closed block	(119.4)	666.2
Amounts outside the closed block that are below investment grade	(75.0)	248.5
Number of securities	230
Total | Fair Value
U.S. government and agency	36.4	41.2
State and political subdivision	19.5	32.3
Foreign government		25.6
Corporate	514.8	868.2
Commercial mortgage-backed ("CMBS")	62.0	184.5
Residential mortgage-backed ("RMBS")	312.4	570.5
CDO/CLO	168.0	183.0
Other asset-backed	57.9	159.1
Debt securities	1,171.0	2,064.4
Equity securities	7.4	12.5
Total temporarily impaired securities	1,178.4	2,076.9
Amounts inside the closed block	501.2	861.2
Amounts outside the closed block	677.2	1,215.7
Amounts outside the closed block that are below investment grade	224.4	317.3
Total | Unrealized Losses
U.S. government and agency	(5.4)	(7.8)
State and political subdivision	(3.1)	(2.9)
Foreign government		(1.7)
Corporate	(86.9)	(171.4)
Commercial mortgage-backed ("CMBS")	(8.3)	(20.0)
Residential mortgage-backed ("RMBS")	(29.3)	(70.6)
CDO/CLO	(30.4)	(53.9)
Other asset-backed	(13.0)	(16.3)
Debt securities	(176.4)	(344.6)
Equity securities	(6.7)	(7.8)
Total temporarily impaired securities	(183.1)	(352.4)
Amounts inside the closed block	(55.8)	(130.2)
Amounts outside the closed block	(127.3)	(222.2)
Amounts outside the closed block that are below investment grade	$ (79.2)	$ (139.1)
Number of securities	300	559