RELATED PARTY TRANSACTIONS: (Details) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2012 item MW	Dec. 31, 2021 USD ($)	Aug. 04, 2014 item
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	$ 48.1			$ 49.1
Related parties payable:	161.1			103.3
Total purchases	1.9	$ 1.4
Total sales	$ 1.6	1.4
Equity investment in affiliate
RELATED PARTY TRANSACTIONS:
Ownership percentage	44.20%
Apu Coropuna S.R.L.
RELATED PARTY TRANSACTIONS:
Ownership percentage	30.00%
Minimum
RELATED PARTY TRANSACTIONS:
Aggregate consideration of Material Affiliate Transaction to be be authorized by the General Counsel and CFO	$ 8.0
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
RELATED PARTY TRANSACTIONS:
Total purchases	399.2	337.9
Total sales	165.8	115.2
Asarco LLC ("Asarco")
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	6.9			10.0
Related parties payable:	32.5			14.9
Total purchases	51.9	23.0
Total sales	32.2	22.8
AMMINCO
RELATED PARTY TRANSACTIONS:
Related parties payable:	8.7			9.5
Total purchases	6.7
Americas Mining Corporation
RELATED PARTY TRANSACTIONS:
Related parties receivable current:				0.1
Compania Perforadora Mexico S.A.P.I. de C.V.
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	0.3			0.3
Eolica El Retiro, S.A.P.I. de C.V.
RELATED PARTY TRANSACTIONS:
Related parties payable:	0.3			2.7
Total purchases	$ 2.5	$ 6.2
Number of wind turbines | item					37
Percentage of supply to third-party energy users	32.50%	61.00%
Ferrocarril Mexicano, S.A. de C.V.
RELATED PARTY TRANSACTIONS:
Related parties payable:	$ 24.5			4.0
Total purchases	32.5	$ 33.1
Grupo Mexico
RELATED PARTY TRANSACTIONS:
Donations	2.6	1.3
Grupo Mexico Servicios
RELATED PARTY TRANSACTIONS:
Related parties payable:	18.6			11.1
Total purchases	15.1	21.9
Total sales		0.1
Intermodal Mexico S.A. de C.V.
RELATED PARTY TRANSACTIONS:
Total purchases		0.5
MGE
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	40.3			38.4
Related parties payable:	68.8			57.2
Total purchases	250.8	209.0
Total sales	$ 133.6	$ 92.3
MGE | Mexico
RELATED PARTY TRANSACTIONS:
Number of natural gas-fired combined cycle power generating units | item			2
Net total capacity (in megawatts) | MW			516.2
Percentage of supply to third-party energy users	1.80%	2.70%
Mexico Compania Constructora S.A de C.V.
RELATED PARTY TRANSACTIONS:
Related parties payable:	$ 5.0			2.0
Mexico Proyectos y Desarrollos SA de CV and affiliates
RELATED PARTY TRANSACTIONS:
Total purchases	38.9	$ 43.8
Peru Mining Exploration And Development Company
RELATED PARTY TRANSACTIONS:
Total purchases		0.4
Grupo Mexico Servicios de Ingenieria, S.A. de C.V.
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	0.2			0.2
Related parties payable:	2.0			0.9
Controladora de Infraestructura Energetica Mexico, S. A. de C. V.
RELATED PARTY TRANSACTIONS:
Total purchases	0.8
Boutique Bowling de Mexico, S.A. de C.V.
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	0.1			0.1
Related parties payable:	0.3			0.3
Total purchases	0.2	0.2
Total sales	0.1
Mexico Transportes Aereos S.A. de C.V. ("Mextransport")
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	0.2
Related parties payable:	0.3			0.5
Total purchases	1.6	1.1
Total sales	1.4	1.4
Operadora de Cinemas S.A. de C.V.
RELATED PARTY TRANSACTIONS:
Related parties receivable current:	0.1
Related parties payable:	0.1			0.2
Total purchases	0.1	0.1
Total sales	0.1
Amminco Apoyo, Ferrocarril Mexicano and Operadora De Cinemas | Maximum
RELATED PARTY TRANSACTIONS:
Related party receivable and payable	0.1			$ 0.1
Amminco Apoyo and Ferrocarril Mexicano | Maximum
RELATED PARTY TRANSACTIONS:
Threshold revenue from related parties	$ 0.1
Boutique Bowling and Operadora De Cinemas | Maximum
RELATED PARTY TRANSACTIONS:
Total sales		$ 0.1