Investments (Aging Of Commercial Mortgage Loans By Property Type) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
30 Days Past Due	$ 13.7	$ 5.5
60 Days Past Due	1.6	9.0
Greater Than 90 Days Past Due	14.0	8.1
Total Past Due	29.3	22.6
Allowance Related to Past Due	(5.3)	(3.2)
Current	5,125.0	4,882.9
Total commercial mortgage loans	5,149.0	4,902.3
Retail [Member]
30 Days Past Due	11.1	3.1
60 Days Past Due	0.3	7.1
Greater Than 90 Days Past Due	7.6	3.0
Total Past Due	19.0	13.2
Allowance Related to Past Due	(3.2)	(1.3)
Current	2,476.4	2,445.9
Total commercial mortgage loans	2,492.2	2,457.8
Office [Member]
30 Days Past Due	1.8	0.8
60 Days Past Due	0	1.5
Greater Than 90 Days Past Due	3.7	1.6
Total Past Due	5.5	3.9
Allowance Related to Past Due	(0.5)	(0.4)
Current	939.7	907.6
Total commercial mortgage loans	944.7	911.1
Industrial [Member]
30 Days Past Due	0.8	1.4
60 Days Past Due	1.3	0.4
Greater Than 90 Days Past Due	1.3	2.3
Total Past Due	3.4	4.1
Allowance Related to Past Due	(0.8)	(0.7)
Current	964.8	897.0
Total commercial mortgage loans	967.4	900.4
Hotels and Motels [Member]
30 Days Past Due	0	0
60 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	0
Allowance Related to Past Due	0	0
Current	297.5	241.9
Total commercial mortgage loans	297.5	241.9
Commercial [Member]
30 Days Past Due	0	0
60 Days Past Due	0	0
Greater Than 90 Days Past Due	1.4	1.2
Total Past Due	1.4	1.2
Allowance Related to Past Due	(0.8)	(0.8)
Current	198.8	186.7
Total commercial mortgage loans	199.4	187.1
Apartment and Other [Member]
30 Days Past Due	0	0.2
60 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	0.2
Allowance Related to Past Due	0	0
Current	247.8	203.8
Total commercial mortgage loans	$ 247.8	$ 204.0