Commitments and Contingencies (Schedule Of Settlement And Defense Costs) (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) claim	Sep. 30, 2019 USD ($) claim	Sep. 30, 2020 USD ($) claim	Sep. 30, 2019 USD ($) claim	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($) claim	Dec. 31, 2017 USD ($)	Mar. 31, 2020 claim	Mar. 31, 2019 claim	Aug. 21, 2012 USD ($)
Loss Contingencies [Line Items]
Pre-tax cash payments			$ 23,700,000	$ 29,000,000.0
Current asbestos liability	$ 65,000,000.0		$ 65,000,000.0		$ 65,000,000.0
Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Estimated Percentage Of Insurance Which Covers Asbestos Costs					14.00%
Asbestos Cumulative Claims Resolved | claim	140,000		140,000
Loss Contingency, Pending Claims, Number | claim	29,308	28,829	29,308	28,829	29,056	29,089		28,927	28,851
Settlement / indemnity costs incurred (1)	$ 2,800,000	$ 8,800,000	$ 18,600,000	$ 38,800,000	$ 45,500,000
Defense costs incurred (1)	3,500,000	5,100,000	11,600,000	15,400,000	20,700,000
Gross Settlement And Defense Incurred Costs	6,300,000	13,900,000	30,200,000	54,200,000	66,200,000
Settlement / indemnity payments	3,100,000	12,000,000.0	20,000,000.0	27,600,000	38,900,000
Defense payments	3,900,000	5,200,000	12,300,000	15,400,000	21,400,000
Insurance receipts	2,400,000	6,200,000	8,600,000	14,100,000	18,800,000
Pre-tax cash payments	4,600,000	11,000,000.0	23,700,000	28,900,000	41,500,000
Cumulative Related Settlement Cost Incurred Before Insurance Recoveries	660,000,000		660,000,000
Cumulative Asbestos Settlement Cost Per Resolved Claim	4,700		4,700
Asbestos Settlement Cost Per Resolved Claim					15,800	$ 11,300	$ 7,800
Estimated Funds Available From Post Bankruptcy Trusts To Pay Current And Future Claimants	36,000,000,000		36,000,000,000
Court Judgment		$ 54,200,000		$ 54,200,000
Increase In Total Asbestos Liability					255,000,000
Insurance Receivable Asbestos	89,000,000		89,000,000		98,000,000
Asbestos Liability	679,000,000		679,000,000		$ 712,000,000
Percentage Of Asbestos Liability Attributable To Settlement And Defense Costs For Future Claims					85.00%
Current asbestos liability	65,000,000		65,000,000
Aggregate Value Of Policy Buy Out Agreements	$ 82,500,000		$ 82,500,000
Ronald Dummitt [Member] | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment										$ 4,900,000