Significant Accounting Policies - Changes in Accumulated Other Comprehensive Loss Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 6,537.6	$ 5,893.3
Other comprehensive (loss) earnings before reclassifications, net of tax	(32.9)	0.3
Amounts reclassified from accumulated other comprehensive loss, net of tax	1.3	2.5
Other comprehensive (loss) earnings, net of tax	(31.6)	2.8
Ending Balance	6,431.1	5,926.7
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(97.6)	(158.1)
Other comprehensive (loss) earnings before reclassifications, net of tax	(33.3)
Amounts reclassified from accumulated other comprehensive loss, net of tax	1.3	2.5
Other comprehensive (loss) earnings, net of tax	(32.0)	2.5
Ending Balance	(129.6)	(155.6)
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(0.3)
Other comprehensive (loss) earnings before reclassifications, net of tax	0.4	0.3
Other comprehensive (loss) earnings, net of tax	0.4	0.3
Ending Balance	0.4
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(97.6)	(158.4)
Ending Balance	$ (129.2)	$ (155.6)