Commitments and Contingencies (Schedule Of Settlement And Defense Costs) (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) claim	Mar. 31, 2020 USD ($) claim	Dec. 31, 2020 USD ($) claim	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Pre-tax cash payments	$ 10,800,000	$ 11,700,000
Estimated Funds Available From Post Bankruptcy Trusts To Pay Current And Future Claimants	36,000,000,000
Current asbestos liability	$ 66,500,000		$ 66,500,000
Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Estimated Percentage Of Insurance Which Covers Asbestos Costs				14.00%
Asbestos Cumulative Claims Resolved | claim	142,000
Loss Contingency, Pending Claims, Number | claim	29,407	29,162	29,138	29,056
Settlement / indemnity costs incurred (1)	$ 5,500,000	$ 8,200,000	$ 35,300,000
Defense costs incurred (1)	3,600,000	4,400,000	15,600,000
Gross Settlement And Defense Incurred Costs	9,100,000	12,600,000	50,900,000
Settlement / indemnity payments	10,100,000	11,000,000.0	24,700,000
Defense payments	3,200,000	4,300,000	16,700,000
Insurance receipts	2,500,000	3,600,000	10,300,000
Pre-tax cash payments	10,800,000	$ 11,700,000	31,100,000
Cumulative Related Settlement Cost Incurred Before Insurance Recoveries	684,000,000
Cumulative Asbestos Settlement Cost Per Resolved Claim	4,800
Asbestos Settlement Cost Per Resolved Claim			13,900	$ 15,800	$ 11,300
Increase In Total Asbestos Liability				255,000,000
Insurance Receivable Asbestos	84,000,000		87,000,000	98,000,000
Asbestos Liability	657,000,000		670,000,000	$ 712,000,000
Percentage Of Asbestos Liability Attributable To Settlement And Defense Costs For Future Claims				85.00%
Current asbestos liability	66,500,000		$ 66,500,000
Aggregate Value Of Policy Buy Out Agreements	$ 82,500,000