Commitments and Contingencies (Asbestos Liability) (Detail)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($) claim	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($) claim	Sep. 30, 2021 USD ($) claim	Sep. 30, 2020 USD ($) claim	Dec. 31, 2020 USD ($) claim	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($)	Jun. 30, 2021 claim	Jun. 30, 2020 claim	Aug. 21, 2012 USD ($)
Loss Contingencies [Line Items]
Payments for asbestos-related fees and costs, net of insurance recoveries				$ 29,600,000	$ 23,700,000
Estimated payments to current and future claimants	$ 36,000,000,000			36,000,000,000
Current portion of total estimated liability	$ 66,500,000			$ 66,500,000		$ 66,500,000
Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Pending claims | claim	29,926		29,308	29,926	29,308	29,138	29,056		29,788	28,927
Gross Settlement And Defense Incurred Costs	$ 14,400,000	$ 50,900,000	$ 6,300,000	$ 35,700,000	$ 30,200,000
Payments for asbestos-related fees and costs, net of insurance recoveries	$ 9,400,000	$ 31,100,000	$ 4,600,000	$ 29,600,000	$ 23,700,000
Cumulative claims resolved | claim	143,000			143,000
Settlement cost	$ 703,000,000			$ 703,000,000
Cumulative Asbestos Settlement Cost Per Resolved Claim	4,900			4,900
Average settlement cost per resolved claim						$ 13,900	$ 15,800	$ 11,300
Additional liability							255,000,000
Liability for claims	630,000,000			630,000,000		670,000,000	$ 712,000,000
Percentage Of Asbestos Liability Attributable To Settlement And Defense Costs For Future Claims							85.00%
Current portion of total estimated liability	66,500,000			66,500,000		66,500,000
Aggregate value of policy buyout agreements	82,500,000			82,500,000
Estimated Percentage Of Insurance Which Covers Asbestos Costs							14.00%
Insurance reimbursement asset	$ 77,000,000			$ 77,000,000		$ 87,000,000	$ 98,000,000
Asbestos Commitments and Contingencies | Ronald Dummitt
Loss Contingencies [Line Items]
Court Judgment											$ 4,900,000
New York | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Pending claims | claim	18,000			18,000
Non-malignancy claims | claim	16,000			16,000