Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Schedule of Investments [Line Items]
Callable bonds without a make-whole provision of fixed maturity available-for-sale securities, percentage	3.70%
Callable bonds without a make-whole provision of fixed maturity available-for-sale securities, amount	$ 288.7
Securities deposited for the benefit of policyholders in accordance with state regulations	7.2		7.2
Interest income recognized on impaired commercial mortgage loans	1.1	1.3
Cash received by the company as interest on impaired commercial mortgage loans	1.1	0.8
Commercial mortgage loans that were at least 60 days past due	4.6		8.6
60 day delinquency proportion of commercial mortgage loan portfolio	0.08%		0.16%
Total fixed maturity securities-available-for-sale	7,885.7		7,773.7
Amount of Commercial Mortgage Loans Granted Forbearance	5.2		5.2
Amount of funding agreements from the Federal Home Loan Bank (FHLB).	158.0		139.0
Amount of the collateral pledged in support of federal home loan bank funding agreements outstanding.	$ 198.7		$ 174.4