Accounting Policies - Reclassifications Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Additional interest expense	$ 129.3	$ 137.1	$ 91.5
Tax effect	136.3	105.7	(94.5)
Earnings from Continuing Operations	11.1	10.5	8.5
Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations	11.1	10.2	7.7
Unamortized Value of Terminated Forward Starting Interest Rate Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations		0.3	0.8
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Settlement charge		2.9
Prior service credit	(0.8)	(2.0)	(1.4)
Actuarial loss	15.5	12.7	13.8
Tax effect	(3.6)	(3.4)	(4.7)
Earnings from Continuing Operations	11.1	10.2	7.7
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefit Plans | Other Nonoperating Expenses and (Income), Net
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications out of accumulated other comprehensive loss before taxes	$ 14.7	13.6	12.4
Reclassification out of Accumulated Other Comprehensive Income | Unamortized Value of Terminated Forward Starting Interest Rate Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Additional interest expense		0.5	1.4
Tax effect		(0.2)	(0.6)
Earnings from Continuing Operations		$ 0.3	$ 0.8