Segments (Segment Information) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Premiums	$ 528.7	$ 539.8	$ 1,630.1	$ 1,610.6
Administrative fees	27.8	28.5	86.2	87.4
Net investment income	159.8	147.3	470.9	456.9
Net capital gains (losses)	(2.6)	7.7	(6.8)	(7.9)
Total revenues	713.7	723.3	2,180.4	2,147.0
Benefits to policyholders	422.4	432.2	1,348.3	1,324.7
Interest credited	43.9	36.7	130.3	117.1
Operating expenses	115.3	120.7	355.9	357.1
Commissions and bonuses	49.6	53.1	156.3	166.1
Premium taxes	9.1	9.1	28.6	27.4
Interest expense	11.8	9.7	31.3	29.2
Net increase in deferred acquisition costs, value of business acquired and intangible assets	0.3	(4.2)	(1.9)	(14.6)
Total benefits and expenses	652.4	657.3	2,048.8	2,007.0
Income (loss) before income taxes	61.3	66.0	131.6	140.0
Total Assets	19,621.3	17,887.9	19,621.3	17,887.9	18,403.2
Insurance Services [Member]
Premiums	527.5	538.3	1,625.1	1,604.4
Administrative fees	3.1	3.0	10.4	8.6
Net investment income	86.0	85.8	254.2	255.6
Net capital gains (losses)	0	0	0	0
Total revenues	616.6	627.1	1,889.7	1,868.6
Benefits to policyholders	417.6	427.1	1,333.3	1,309.5
Interest credited	1.0	0.9	3.6	3.5
Operating expenses	85.4	84.2	264.5	256.4
Commissions and bonuses	43.2	46.1	133.9	140.3
Premium taxes	9.1	9.1	28.6	27.3
Interest expense	0	0	0	0
Net increase in deferred acquisition costs, value of business acquired and intangible assets	(2.1)	(5.3)	(6.0)	(16.3)
Total benefits and expenses	554.2	562.1	1,757.9	1,720.7
Income (loss) before income taxes	62.4	65.0	131.8	147.9
Total Assets	8,347.5	8,109.5	8,347.5	8,109.5
Asset Management [Member]
Premiums	1.2	1.5	5.0	6.2
Administrative fees	29.2	29.7	89.1	91.2
Net investment income	72.3	59.0	210.0	193.5
Net capital gains (losses)	0	0	0	0
Total revenues	102.7	90.2	304.1	290.9
Benefits to policyholders	4.8	5.1	15.0	15.2
Interest credited	42.9	35.8	126.7	113.6
Operating expenses	28.7	28.9	88.2	87.2
Commissions and bonuses	6.4	7.0	22.4	25.8
Premium taxes	0	0	0	0.1
Interest expense	0	0	0	0
Net increase in deferred acquisition costs, value of business acquired and intangible assets	2.4	1.1	4.1	1.7
Total benefits and expenses	85.2	77.9	256.4	243.6
Income (loss) before income taxes	17.5	12.3	47.7	47.3
Total Assets	10,888.7	9,492.9	10,888.7	9,492.9
Other Category [Member]
Administrative fees	(4.5)	(4.2)	(13.3)	(12.4)
Net investment income	1.5	2.5	6.7	7.8
Net capital gains (losses)	(2.6)	7.7	(6.8)	(7.9)
Total revenues	(5.6)	6.0	(13.4)	(12.5)
Benefits to policyholders	0	0	0	0
Interest credited	0	0	0	0
Operating expenses	1.2	7.6	3.2	13.5
Commissions and bonuses	0	0	0	0
Premium taxes	0	0	0	0
Interest expense	11.8	9.7	31.3	29.2
Net increase in deferred acquisition costs, value of business acquired and intangible assets	0	0	0	0
Total benefits and expenses	13.0	17.3	34.5	42.7
Income (loss) before income taxes	(18.6)	(11.3)	(47.9)	(55.2)
Total Assets	$ 385.1	$ 285.5	$ 385.1	$ 285.5