Significant Accounting Policies - Reclassifications Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax effect	$ 109.9	$ 79.2	$ 237.4	$ 189.4
Earnings from Continuing Operations	1.1	4.9	3.1	7.9
Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations	1.1	4.9	3.1	7.9
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Settlement charge	0.0	4.5	0.0	4.5
Prior service cost	1.4	1.1	4.2	3.2
Actuarial loss	(0.1)	0.9	0.0	2.8
Tax effect	(0.4)	(1.6)	(1.1)	(2.6)
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefit Plans | Other Nonoperating Income, Net
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications out of accumulated other comprehensive loss before taxes	$ 1.5	$ 6.5	$ 4.2	$ 10.5