Retirement Benefits - Schedule of Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Actuarial gains		$ (2.3)
Amortization of actuarial losses	[1]	0.4
Cumulative translation adjustments		(0.4)
Total other comprehensive income (loss), before tax		(2.3)
Deferred income taxes		0.6
Total other comprehensive income (loss), net of tax		4.3	$ (14.3)	$ 10.8
Net Actuarial Gain (Loss)
Defined Benefit Plan Disclosure [Line Items]
Total other comprehensive income (loss), net of tax		$ (1.7)	$ 2.6	$ (1.0)

[1] Reflects amounts reclassified from accumulated other comprehensive income (loss) to net income.