Significant Accounting Policies - Reclassifications Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	$ 91.9	$ 104.4	$ 127.5	$ 110.2
Earnings from Continuing Operations	1.2	1.7	2.1	3.0
Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations	1.2	1.7	2.1	3.0
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service cost	1.6	1.2	2.8	2.1
Actuarial loss	0.0	1.1	0.0	1.9
Tax benefit	(0.4)	(0.6)	(0.7)	(1.0)
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	$ 1.6	$ 2.3	$ 2.8	$ 4.0