Investments (Aging Of Commercial Mortgage Loans By Property Type) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 5.0	$ 11.4
Past Due	(2.2)	(2.3)
Current	5,544.5	5,312.0
Total commercial mortgage loans	5,547.3	5,321.1
30 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1.9	2.8
60 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	2.7
Greater Than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3.1	5.9
Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3.7	7.0
Past Due	(1.9)	(2.1)
Current	2,712.4	2,622.2
Total commercial mortgage loans	2,714.2	2,627.1
Retail [Member] | 30 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1.3	0.2
Retail [Member] | 60 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	2.0
Retail [Member] | Greater Than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2.4	4.8
Office [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	2.7
Past Due	0.0	0.0
Current	1,059.3	1,010.7
Total commercial mortgage loans	1,059.3	1,013.4
Office [Member] | 30 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	1.9
Office [Member] | 60 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Office [Member] | Greater Than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.8
Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1.3	0.8
Past Due	(0.3)	(0.2)
Current	1,040.4	1,000.9
Total commercial mortgage loans	1,041.4	1,001.5
Industrial [Member] | 30 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.6	0.5
Industrial [Member] | 60 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Industrial [Member] | Greater Than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.7	0.3
Hotels and Motels [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Past Due	0.0	0.0
Current	204.5	165.7
Total commercial mortgage loans	204.5	165.7
Hotels and Motels [Member] | 30 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Hotels and Motels [Member] | 60 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Hotels and Motels [Member] | Greater Than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Past Due	0.0	0.0
Current	211.0	213.6
Total commercial mortgage loans	211.0	213.6
Commercial [Member] | 30 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Commercial [Member] | 60 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Commercial [Member] | Greater Than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Apartment and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.9
Past Due	0.0	0.0
Current	316.9	298.9
Total commercial mortgage loans	316.9	299.8
Apartment and Other [Member] | 30 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.2
Apartment and Other [Member] | 60 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.7
Apartment and Other [Member] | Greater Than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0.0	$ 0.0