CONSOLIDATED INCOME STATEMENTS (unaudited) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Income Statement [Abstract]
Revenue	$ 2,166	$ 1,802	$ 6,248	$ 5,614
Cost of sales (excluding depreciation and amortization)	(1,852)	(1,597)	(5,408)	(4,884)
Depreciation and amortization	(84)	(76)	(244)	(227)
Selling and administrative expenses	(85)	(66)	(251)	(221)
Research and development expenses	(12)	(11)	(37)	(39)
Other gains and losses - net	20	(2)	19	(7)
Finance costs - net	(27)	(31)	(83)	(83)
Income before tax	126	19	244	153
Income tax expense	(38)	(11)	(82)	(46)
Net income	88	8	162	107
Attributable to:
Equity holders of Constellium	88	7	161	104
Non-controlling interests	0	1	1	3
Net income	$ 88	$ 8	$ 162	$ 107
Earnings per share attributable to the equity holders of Constellium (in U.S. dollars)
Basic earnings per share (in USD per share)	$ 0.63	$ 0.05	$ 1.14	$ 0.72
Diluted earnings per share (in USD per share)	$ 0.62	$ 0.05	$ 1.13	$ 0.70

Other Operating And Nonoperating Gains (Losses)

No definition available.

Name:	cstm_OtherOperatingAndNonoperatingGainsLosses
Namespace Prefix:	cstm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Cost of product sold and service rendered, excluding depreciation, depletion, and amortization.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(2)(a))
-SubTopic 10
-Topic 220
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(2)(d))
-SubTopic 10
-Topic 220
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2