Comprehensive Income - Reclassifications from Accumulated Other Comprehensive Loss Amortization of Pension Plan Cost (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before taxes		$ 0.5	$ 0.8	$ 1.4	$ 1.6
Income tax expense (benefit)		0.1	0.3	0.4	0.5
Reclassifications, net of tax		0.4	0.5	1.0	1.1
Accumulated Defined Benefit Plans Adjustment, Net Actuarial loss
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before taxes	[1]	1.0	$ 0.8	1.9	$ 1.6
Translation Adjustments
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before taxes	[2]	$ (0.5)		$ (0.5)

[1] These accumulated other comprehensive loss components are included in the calculation of net periodic pension and other postretirement benefits plan income recognized in investment and other income, net in the Unaudited Condensed Consolidated Statements of Operations (see Note 6, Retirement Plans).

[2] Translation adjustment reclassification resulting from the liquidation of a foreign subsidiary is included in investment and other income, net in the Unaudited Condensed Consolidated Statements of Operations.