RELATED PARTY TRANSACTIONS: (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2020 MWh	Dec. 31, 2012 item MW	Dec. 31, 2014 item
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	$ 13.5	$ 27.3
Affiliates
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	13.5	27.3
Other accrued liabilities	49.2	93.6
Total purchases	367.2	418.2	$ 534.6
Total sales	$ 2.9	3.0	2.1
Affiliates | Equity investment in affiliate
RELATED PARTY TRANSACTIONS:
Ownership percentage	44.20%
Affiliates | Apu Coropuna S.R.L.
RELATED PARTY TRANSACTIONS:
Ownership percentage	30.00%
Affiliates | Minimum
RELATED PARTY TRANSACTIONS:
Aggregate consideration of Material Affiliate Transaction to be be authorized by the General Counsel and CFO	$ 8.0
Affiliates | Maximum
RELATED PARTY TRANSACTIONS:
Aggregate consideration of Material Affiliate Transaction to be be authorized by the General Counsel and CFO	10.0
Grupo Mexico and affiliates | Affiliates
RELATED PARTY TRANSACTIONS:
Total sales	73.9	105.9	213.0
Asarco LLC ("Asarco") | Affiliates
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	7.1	9.4
Other accrued liabilities	6.0	13.8
Total purchases	4.7	30.4	66.3
Total sales	38.0	39.6	48.0
AMMINCO Apoyo Administrativo, S.A. de C.V. ("AMMINCO") | Affiliates
RELATED PARTY TRANSACTIONS:
Other accrued liabilities	6.0	5.0
Total purchases	10.0	10.0	10.0
Total sales	0.1
Controladora de Infraestructura Energetica Mexico, S. A. de C. V. | Affiliates
RELATED PARTY TRANSACTIONS:
Total purchases			0.8
Eolica El Retiro, S.A.P.I. de C.V.
RELATED PARTY TRANSACTIONS:
Number of wind turbines | item						37
Eolica El Retiro, S.A.P.I. de C.V. | Affiliates
RELATED PARTY TRANSACTIONS:
Other accrued liabilities	0.4	0.2
Total purchases	$ 4.9	$ 2.3	3.0
Percentage of supply to third-party energy users	25.50%	12.00%
Ferrocarril Mexicano, S.A. de C.V. | Affiliates
RELATED PARTY TRANSACTIONS:
Other accrued liabilities	$ 2.9	$ 7.9
Total purchases	48.4	53.0	42.9
Grupo Mexico | Affiliates
RELATED PARTY TRANSACTIONS:
Total purchases	3.4	3.9	2.7
Donations	2.6	4.3	3.5
Grupo Mexico Servicios | Affiliates
RELATED PARTY TRANSACTIONS:
Other accrued liabilities	4.3	2.7
Total purchases	20.1	20.1	20.1
Mexico Generadora de Energia S. de R.L. ("MGE") | Mexico
RELATED PARTY TRANSACTIONS:
Number of natural gas-fired combined cycle power generating units | item					2
Mexico Generadora de Energia S. de R.L. ("MGE") | Affiliates
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	5.4	17.1
Other accrued liabilities	15.9	50.3
Total purchases	172.6	224.6	331.0
Total sales	$ 35.8	$ 66.3	165.0
Mexico Generadora de Energia S. de R.L. ("MGE") | Affiliates | Mexico
RELATED PARTY TRANSACTIONS:
Net total capacity (in megawatts) | MW					516.2
Percentage of supply to third-party energy users	20.20%	7.60%
Mexico Compania Constructora S.A de C.V. | Affiliates
RELATED PARTY TRANSACTIONS:
Other accrued liabilities	$ 8.0	$ 9.5
Total purchases	75.3	59.8	43.8
Parque Eolico de Fenicias, S. de R.L. de C.V. | Affiliates
RELATED PARTY TRANSACTIONS:
Other accrued liabilities	2.6
Total purchases	$ 12.4
Purchase agreement, contracted power capacity (in megawatts per year) | MWh				611,400
Term of power purchase agreement related to sale of power plant				20 years
Percentage of supply to third-party energy users	58.60%
Grupo Mexico Servicios de Ingenieria, S.A. de C.V. | Affiliates
RELATED PARTY TRANSACTIONS:
Other accrued liabilities	$ 2.1	3.5
Total purchases	18.8	18.0	16.7
AMMINCO, Ferrocarril Mexicano, S.A. de C.V. & Mexico Compania Constructora S.A de C.V. | Affiliates | Maximum
RELATED PARTY TRANSACTIONS:
Related party receivable and payable	0.1	0.1
AMMINCO & Ferrocarril Mexicano, S.A. de C.V. | Affiliates | Maximum
RELATED PARTY TRANSACTIONS:
Threshold revenue from related parties	0.1	0.1	0.1
Boutique Bowling de Mexico, S.A. de C.V. | Affiliates
RELATED PARTY TRANSACTIONS:
Other accrued liabilities	0.5	0.3
Total purchases	0.6	0.7	0.4
Total sales	0.1	0.1	0.1
Empresarios Industriales de Mexico, S.A. de C.V | Affiliates
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	0.9	0.6
Total sales	0.4	0.5
Mexico Transportes Aereos S.A. de C.V. ("Mextransport") | Affiliates
RELATED PARTY TRANSACTIONS:
Related parties receivable current:		0.1
Other accrued liabilities	0.1	0.3
Total purchases	2.5	2.8	2.1
Total sales	2.3	2.3	1.9
Operadora de Cinemas S.A. de C.V. | Affiliates
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	0.1	0.1
Other accrued liabilities	0.4	0.1
Total purchases	0.3	0.4	0.2
Total sales	$ 0.1	$ 0.1	$ 0.1