Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income	$ 124.0	$ 109.8	$ 377.6	$ 259.2
Other comprehensive income (loss)
Foreign currency translation adjustments	(2.0)	10.4	(13.5)	4.7
Unrealized gain (loss) on investments, net of tax	0.2	0.4	0.3	0.8
Defined benefit pension plans:
Amortization of amounts included in net periodic benefit cost, net of tax	1.2	1.2	3.8	3.3
Other comprehensive income (loss)	(0.7)	11.4	(9.2)	7.8
Comprehensive income	123.3	121.2	368.4	267.0
Actuarial loss, net of tax
Defined benefit pension plans:
Change benefit obligations, translation adjustment	(0.1)	(0.4)	0.2	(0.8)
Amortization of amounts included in net periodic benefit cost, net of tax	1.1	0.9	3.4	2.6
Other comprehensive income (loss)	1.0	0.5	3.6	1.8
Prior service cost, net of tax
Defined benefit pension plans:
Amortization of amounts included in net periodic benefit cost, net of tax	0.1	0.2	0.3	0.6
Other comprehensive income (loss)	0.1	0.2	0.3	0.6
Other
Defined benefit pension plans:
Amortization of amounts included in net periodic benefit cost, net of tax	0.0	0.1	0.1	0.1
Other comprehensive income (loss)	$ 0.0	$ (0.1)	$ 0.1	$ (0.1)