Fair Value (Summary Gains and Losses due to Changes in Fair Value Recorded in Income) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Fair Value [Line Items]
Net realized investment gains (losses)	$ 0.1	$ (0.1)	$ 0.1
Level 3 | Net Realized Investment Gains [Member]
Fair Value [Line Items]
Net realized investment gains (losses)	0.1	0.1	0.1
Level 3 | Other Than Temporary Impairments [Member]
Fair Value [Line Items]
Net realized investment gains (losses)		(0.2)
Level 3 | Corporate [Member] | Net Realized Investment Gains [Member]
Fair Value [Line Items]
Net realized investment gains (losses)	$ 0.1		$ 0.1
Level 3 | Corporate [Member] | Other Than Temporary Impairments [Member]
Fair Value [Line Items]
Net realized investment gains (losses)		(0.2)
Level 3 | Municipal [Member] | Net Realized Investment Gains [Member]
Fair Value [Line Items]
Net realized investment gains (losses)		$ 0.1