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Commitments and Contingencies (Litigation) (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Commitments and Contingencies Disclosure [Abstract] |  |
Asbestos Litigation Reserve | $ 9 | $ 12
Insurance Settlements Receivable | $ 4 | $ 6

X
- Definition Aggregate carrying amount as of the balance sheet date of reserves for the costs of settling asbestos claims, undiscounted. + References No definition available. + Details
Name: | neu_AsbestosLitigationReserve
Namespace Prefix: | neu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount due in settlement of a claim for reimbursement from an insurance company when the Company has suffered a loss covered under an insurance policy. + References No definition available. + Details
Name: | us-gaap_InsuranceSettlementsReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant