Significant Accounting Policies - Changes in Accumulated Other Comprehensive Loss Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, Total Equity	$ 6,431.0	$ 5,926.7	$ 6,537.6	$ 5,893.3
Amounts reclassified from accumulated other comprehensive loss, net of tax	(1.7)	2.1
Other comprehensive (loss) earnings, net of tax	1.2	2.6	(30.5)	5.4
Ending Balance, Total Equity	6,772.1	6,128.2	6,772.1	6,128.2
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, Total Equity	(129.7)	(155.6)	(97.6)	(158.1)
Other comprehensive (loss) earnings before reclassifications, net of tax	0.4		(33.0)
Amounts reclassified from accumulated other comprehensive loss, net of tax	(1.7)	2.1	(3.0)	4.6
Other comprehensive (loss) earnings, net of tax	2.1	2.1	(30.0)	4.6
Ending Balance, Total Equity	(127.6)	(153.5)	(127.6)	(153.5)
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, Total Equity	0.4			(0.3)
Other comprehensive (loss) earnings before reclassifications, net of tax	(0.9)	0.5	(0.5)	0.8
Other comprehensive (loss) earnings, net of tax	(0.9)	0.5	(0.5)	0.8
Ending Balance, Total Equity	(0.5)	0.5	(0.5)	0.5
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, Total Equity	(129.3)	(155.6)	(97.6)	(158.4)
Other comprehensive (loss) earnings before reclassifications, net of tax	(0.5)	0.5	(33.5)	0.8
Amounts reclassified from accumulated other comprehensive loss, net of tax	(1.7)		(3.0)	4.6
Other comprehensive (loss) earnings, net of tax	1.2		(30.5)	5.4
Ending Balance, Total Equity	$ (128.1)	$ (153.0)	$ (128.1)	$ (153.0)