Redeemable Noncontrolling Interest (Details) $ in Millions		3 Months Ended		9 Months Ended			12 Months Ended
		Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) shares		Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) shares	Apr. 01, 2021
Increase (Decrease) in Temporary Equity [Roll Forward]
Balance, Beginning of period				$ 214.5	[1]	$ 503.7	$ 503.7
Net income attributable to NCI		$ 1.9	$ 1.8	5.9		10.6	5.7
Other comprehensive income (loss) attributable to NCI1		0.9	(0.4)	5.8		(5.0)	(3.3)
Exercise of employee stock options				7.7		9.4	9.4
Purchase/change of ARX minority shares				(11.2)		(298.2)	(298.2)
Change in redemption value of NCI				0.2		(3.1)	(2.8)
Balance, End of period	[1]	$ 222.9	$ 217.4	$ 222.9		$ 217.4	$ 214.5
ARX Holding Corp.
Redeemable Noncontrolling Interest [Line Items]
Number of Shares Put Pursuant to Stockholders' Agreement | shares							204,527
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | shares							5,483
Payments to Acquire Interest in Subsidiaries and Affiliates							$ 295.9
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage		87.10%	86.80%	87.10%		86.80%	86.80%
Shares held in Employee Stock Option Plan, Suspense Shares | shares		10,438		10,438
Employee Stock Ownership Plan (ESOP), Deferred Shares, Fair Value		$ 15.8		$ 15.8
Scenario, Forecast | ARX Holding Corp.
Redeemable Noncontrolling Interest [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage								100.00%

[1] See Note 12 – Redeemable Noncontrolling Interest for further discussion.