Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (57.3)	$ 144.4	$ 206.7	$ 534.1
Other comprehensive (loss) income:
Change in unrealized gains on securities, net of taxes of $4.0, $(8.4), $(53.7) and $(85.7), respectively	(7.7)	16.3	98.6	162.1
Change in other-than-temporary impairment gains, net of taxes of $0.5, $(0.2), $1.5 and $0.4, respectively	(1.0)	0.3	(2.8)	(0.8)
Change in foreign currency translation, net of taxes of $(1.5), $0.5, $(2.8) and $(1.2), respectively	27.6	(15.9)	65.1	(18.6)
Amortization of pension and postretirement unrecognized net periodic benefit cost, net of taxes of $(0.3), $(0.1), $(0.5) and $(36.0), respectively	0.6	0.2	0.9	66.8
Total other comprehensive income	19.5	0.9	161.8	209.5
Total comprehensive (loss) income	$ (37.8)	$ 145.3	$ 368.5	$ 743.6