Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 112.8	$ 173.2	$ 231.7
Other comprehensive income (loss), before tax:
Unrealized gains/losses on securities	257.8	(693.4)	531.8
Other-than-temporary impairments	8.7	2.8	5.1
Pension and other post-employment benefits liability	(1.4)	(2.3)	(2.2)
Other comprehensive income (loss), before tax	265.1	(692.9)	534.7
Income tax expense (benefit) related to items of other comprehensive income (loss)	92.4	(238.2)	188.6
Other comprehensive income (loss), after tax	172.7	(454.7)	346.1
Comprehensive income (loss)	$ 285.5	$ (281.5)	$ 577.8