Accounting Policies - Components of Changes in Accumulated Other Comprehensive Loss and Related Cumulative Noncurrent Deferred Tax Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 7,172.8	$ 6,537.6	$ 5,893.3
Ending Balance	8,035.6	7,172.8	6,537.6
Cumulative noncurrent deferred tax assets at end of period	53.8	50.1
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(36.5)	(97.6)	(158.1)
Other comprehensive (loss) earnings before reclassifications, net of Tax	(15.7)	51.6	51.3
Amounts reclassified from accumulated other comprehensive loss, net of tax	4.2	9.5	9.2
Other comprehensive earnings (loss), net of tax	(11.5)	61.1	60.5
Ending Balance	(48.0)	(36.5)	(97.6)
Cumulative noncurrent deferred tax assets at end of period	53.8	50.1	69.7
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(2.0)	0.0	(0.3)
Other comprehensive (loss) earnings before reclassifications, net of Tax	0.8	(2.0)	0.3
Amounts reclassified from accumulated other comprehensive loss, net of tax	0.0	0.0	0.0
Other comprehensive earnings (loss), net of tax	0.8	(2.0)	0.3
Ending Balance	(1.2)	(2.0)	0.0
Cumulative noncurrent deferred tax assets at end of period	0.0	0.0	0.0
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(38.5)	(97.6)	(158.4)
Other comprehensive (loss) earnings before reclassifications, net of Tax	(14.9)	49.6	51.6
Amounts reclassified from accumulated other comprehensive loss, net of tax	4.2	9.5	9.2
Other comprehensive earnings (loss), net of tax	(10.7)	59.1	60.8
Ending Balance	(49.2)	(38.5)	(97.6)
Cumulative noncurrent deferred tax assets at end of period	$ 53.8	$ 50.1	$ 69.7