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Commitments and Contingencies (Litigation) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
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

X

- 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