Significant Accounting Policies - Reclassifications Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	$ 104.4	$ 62.3	$ 110.2	$ 78.1
Earnings from Continuing Operations	(1.7)	2.1
Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations	(1.7)	2.1	(3.0)	4.6
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service credit	1.2	0.1	2.1
Actuarial loss	(1.1)	2.8	(1.9)	6.1
Tax benefit	(0.6)	(0.8)	(1.0)	(1.5)
Earnings from Continuing Operations		2.1	(3.0)	4.6
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	$ 2.3	$ 2.9	$ 4.0	$ 6.1