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- Details

Name:	us-gaap_DebtInstrumentAxis=nvl_A6.375SeniorNotesDueAugust2033Member
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Debt - Schedule of Debt (Details) ¥ in Millions, SFr in Millions, $ in Millions	Dec. 31, 2025 USD ($)	Dec. 31, 2025 CNY (¥)	Dec. 31, 2025 CHF (SFr)	Aug. 18, 2025 USD ($)	Jun. 30, 2025	Mar. 31, 2025 USD ($)	Mar. 31, 2025 CNY (¥)	Mar. 31, 2025 CHF (SFr)	Dec. 31, 2024 CNY (¥)
Debt Instrument
Short-term borrowings	$ (592)					$ (348)
Long-term debt, principal	6,385					5,832
Long-term debt, Unamortized Carrying Value Adjustments	0					0
Less: Current portion of long-term debt	0					0
Unamortized Carrying Value Adjustments	(68)					(59)
Long-term debt, Carrying Value	6,342					5,790
Current portion of long-term debt	(52)					(32)
Long-term debt, net of current portion, Carrying Value	6,317					5,773
Total debt	7,029					6,212
Total debt, Carrying Value	$ 6,961					6,153
China Bank Loans, due August 2027
Debt Instrument
Stated rate	2.65%	2.65%	2.65%
Long-term debt, principal	$ 37	¥ 260				41	¥ 300
Long-term debt, Unamortized Carrying Value Adjustments	0					0
Long-term debt, Carrying Value	$ 37					41
China Loan, due September 2027
Debt Instrument
Stated rate	2.45%	2.45%	2.45%
Long-term debt, principal	$ 14	¥ 100				13	100
Long-term debt, Unamortized Carrying Value Adjustments	0					0
Long-term debt, Carrying Value	$ 14					13
China Loan, due November 2027
Debt Instrument
Stated rate	2.60%	2.60%	2.60%
Long-term debt, principal	$ 21	¥ 149				21	150		¥ 150
Long-term debt, Unamortized Carrying Value Adjustments	0					0
Long-term debt, Carrying Value	$ 21					21
China Loan, due December 2027
Debt Instrument
Stated rate	2.50%	2.50%	2.50%
Long-term debt, principal	$ 21	¥ 149				21	¥ 150		¥ 150
Long-term debt, Unamortized Carrying Value Adjustments	0					0
Long-term debt, Carrying Value	$ 21					21
Sierre Loan, due October 2027
Debt Instrument
Stated rate	0.42%	0.42%	0.42%
Long-term debt, principal	$ 126		SFr 100			113		SFr 100
Long-term debt, Unamortized Carrying Value Adjustments	0					0
Long-term debt, Carrying Value	$ 126					113
Interest rate, effective percentage					0.50%
Series 2025A Bonds, due June 2032
Debt Instrument
Stated rate	5.00%	5.00%	5.00%
Long-term debt, principal	$ 400					0
Long-term debt, Unamortized Carrying Value Adjustments	(6)					0
Long-term debt, Carrying Value	$ 394					0
Series 2025 B Bonds, due June 2032
Debt Instrument
Stated rate	4.625%	4.625%	4.625%
Long-term debt, principal	$ 100					0
Long-term debt, Unamortized Carrying Value Adjustments	(2)					0
Long-term debt, Carrying Value	$ 98					0
Finance lease obligations and other debt, due through April 2040
Debt Instrument
Stated rate	4.87%	4.87%	4.87%
Long-term debt, principal	$ 27					15
Long-term debt, Unamortized Carrying Value Adjustments	0					0
Long-term debt, Carrying Value	$ 27					15
Term Loan \| Floating rate Term Loans, due March 2032
Debt Instrument
Stated rate	5.42%	5.42%	5.42%
Long-term debt, principal	$ 1,241					1,250
Long-term debt, Unamortized Carrying Value Adjustments	(15)					(16)
Long-term debt, Carrying Value	$ 1,226					1,234
Senior Notes \| Senior Notes due November 2026
Debt Instrument
Stated rate	3.25%	3.25%	3.25%
Long-term debt, principal	$ 13					750
Long-term debt, Unamortized Carrying Value Adjustments	0					(3)
Long-term debt, Carrying Value	$ 13			$ 750		747
Senior Notes \| Senior Notes due April 2029
Debt Instrument
Stated rate	3.375%	3.375%	3.375%
Long-term debt, principal	$ 587					540
Long-term debt, Unamortized Carrying Value Adjustments	(5)					(7)
Long-term debt, Carrying Value	$ 582					533
Senior Notes \| Senior Notes Due 2030
Debt Instrument
Stated rate	4.75%	4.75%	4.75%
Long-term debt, principal	$ 1,600					1,600
Long-term debt, Unamortized Carrying Value Adjustments	(13)					(15)
Long-term debt, Carrying Value	1,587					1,585
Senior Notes \| 6.875% Senior Notes, due January 2030
Debt Instrument
Long-term debt, principal	750					750
Long-term debt, Unamortized Carrying Value Adjustments	(10)					(11)
Long-term debt, Carrying Value	$ 740					739
Interest rate, effective percentage	6.875%	6.875%	6.875%
Senior Notes \| Senior Notes due August 2031
Debt Instrument
Stated rate	3.875%	3.875%	3.875%
Long-term debt, principal	$ 750					750
Long-term debt, Unamortized Carrying Value Adjustments	(6)					(7)
Long-term debt, Carrying Value	$ 744					743
Senior Notes \| 6.375% Senior Notes due August 2033
Debt Instrument
Stated rate	6.375%	6.375%	6.375%
Long-term debt, principal	$ 750					0
Long-term debt, Unamortized Carrying Value Adjustments	(11)					0
Long-term debt, Carrying Value	$ 739					$ 0