Commitments and Contingencies (Other Contingencies) (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2014 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2012 a
Environmental Claims For A Site In Goodyear Arizona
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Revision in Estimates	$ 49.0	$ 18.9
Estimated liability			$ 37.5	$ 39.8
Accrued environmental loss contingencies current			$ 10.9	10.9
Loss Contingency Reimbursement Rate			21.00%
Other receivables			$ 7.3	$ 7.8
Environmental Claims For Crab Orchard National Wildlife Refuge Superfund Site
Loss Contingencies [Line Items]
Approximate Size Of Referenced Site | a					55,000