Investments (Performing And Nonperforming Commercial Mortgage Loans By Property Type) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Commercial mortgage loans, net	$ 5,149.0	$ 4,902.3
Performing Financing Receivable [Member]
Commercial mortgage loans, net	5,138.6	4,861.1
Nonperforming Financing Receivable [Member]
Commercial mortgage loans, net	10.4	41.2
Retail [Member]
Commercial mortgage loans, net	2,492.2	2,457.8
Retail [Member] | Performing Financing Receivable [Member]
Commercial mortgage loans, net	2,487.5	2,442.3
Retail [Member] | Nonperforming Financing Receivable [Member]
Commercial mortgage loans, net	4.7	15.5
Office [Member]
Commercial mortgage loans, net	944.7	911.1
Office [Member] | Performing Financing Receivable [Member]
Commercial mortgage loans, net	941.5	898.4
Office [Member] | Nonperforming Financing Receivable [Member]
Commercial mortgage loans, net	3.2	12.7
Industrial [Member]
Commercial mortgage loans, net	967.4	900.4
Industrial [Member] | Performing Financing Receivable [Member]
Commercial mortgage loans, net	965.5	895.2
Industrial [Member] | Nonperforming Financing Receivable [Member]
Commercial mortgage loans, net	1.9	5.2
Hotels and Motels [Member]
Commercial mortgage loans, net	297.5	241.9
Hotels and Motels [Member] | Performing Financing Receivable [Member]
Commercial mortgage loans, net	297.5	241.9
Hotels and Motels [Member] | Nonperforming Financing Receivable [Member]
Commercial mortgage loans, net	0	0
Commercial [Member]
Commercial mortgage loans, net	199.4	187.1
Commercial [Member] | Performing Financing Receivable [Member]
Commercial mortgage loans, net	198.8	182.0
Commercial [Member] | Nonperforming Financing Receivable [Member]
Commercial mortgage loans, net	0.6	5.1
Apartment and Other [Member]
Commercial mortgage loans, net	247.8	204.0
Apartment and Other [Member] | Performing Financing Receivable [Member]
Commercial mortgage loans, net	247.8	201.3
Apartment and Other [Member] | Nonperforming Financing Receivable [Member]
Commercial mortgage loans, net	$ 0	$ 2.7