Investments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Net unrealized gains on impaired securities	$ 18.2		$ 18.2		$ 21.4
Restricted assets, fixed maturities	596.0		596.0
Restricted assets, cash and cash equivalents	5.0		5.0
Other-than-temporary impairments	1.6	$ 0.1	5.0	$ 19.2
Other-than-temporary impairments recorded as unrealized losses in AOCI	0.3		0.5	6.8
Other-than-temporary impairments recognized in earnings	$ 1.3	$ 0.1	$ 4.5	$ 26.0