SEGMENT AND RELATED INFORMATION: - Financial (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) segment item country	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Financial information related to segments
Number of reportable segments | segment	3
Number of countries having open-pit operations | country	2
Financial information relating to segments
Net sales	$ 11,433.4	$ 9,895.8	$ 10,047.9
Cost of sales (exclusive of depreciation, amortization and depletion)	4,841.4	4,687.7	4,649.1
Selling, general and administrative	130.5	127.2	125.0
Depreciation, amortization and depletion	845.9	833.6	796.3
Exploration	60.9	55.0	41.7
Operating income	5,554.7	4,192.3	4,435.8
Interest, net	(202.7)	(240.1)	(305.1)
Other income (expense)	5.5	3.6	117.1
Income before income taxes	5,357.4	3,955.8	4,247.8
Capital investment	1,027.3	1,008.6	948.5
Property and mine development, net	9,883.3	9,782.9	9,596.6
Total assets	18,713.5	16,725.3	17,277.4
Operating segment
Financial information relating to segments
Net sales	11,625.8	10,047.4	10,347.6
Cost of sales (exclusive of depreciation, amortization and depletion)	5,038.0	4,845.4	4,966.0
Selling, general and administrative	121.4	118.9	115.3
Depreciation, amortization and depletion	808.2	795.2	756.3
Exploration	52.4	43.9	27.0
Operating income	5,605.8	4,244.0	4,483.1
Capital investment	1,015.8	992.2	939.5
Property and mine development, net	9,296.1	8,965.3	8,850.4
Total assets	15,087.9	14,497.2	14,807.4
Intersegment sale
Financial information relating to segments
Net sales		(151.6)	(299.7)
Corporate, other and eliminations
Financial information relating to segments
Net sales	(192.4)	(151.6)	(299.7)
Cost of sales (exclusive of depreciation, amortization and depletion)	(196.5)	(157.7)	(316.9)
Selling, general and administrative	9.1	8.3	9.7
Depreciation, amortization and depletion	37.7	38.4	40.0
Exploration	8.5	11.1	14.7
Operating income	(51.1)	(51.7)	(47.3)
Capital investment	11.5	16.4	9.0
Property and mine development, net	587.2	817.6	746.2
Total assets	3,625.6	2,228.1	2,470.0
Reportable subsegments | Operating segment
Financial information relating to segments
Net sales	11,433.4	9,895.8	10,047.9
Intersegment sales | Operating segment
Financial information relating to segments
Net sales	192.4	151.6	299.7
Intersegment sales | Intersegment sale
Financial information relating to segments
Net sales	$ (192.4)
Mexican Open-Pit
Financial information related to segments
Number of open-pit copper mines | item	2
Mexican Open-Pit | Operating segment
Financial information relating to segments
Net sales	$ 6,317.0	5,562.3	5,772.6
Cost of sales (exclusive of depreciation, amortization and depletion)	2,447.5	2,325.1	2,371.9
Selling, general and administrative	70.9	70.1	65.9
Depreciation, amortization and depletion	405.8	386.1	377.0
Exploration	8.7	6.2	3.1
Operating income	3,384.1	2,774.8	2,954.7
Capital investment	621.9	521.8	422.7
Property and mine development, net	4,735.4	4,590.1	4,512.6
Total assets	8,605.1	8,695.6	8,835.9
Mexican Open-Pit | Reportable subsegments | Operating segment
Financial information relating to segments
Net sales	6,305.1	5,562.3	5,610.9
Mexican Open-Pit | Intersegment sales | Operating segment
Financial information relating to segments
Net sales	$ 11.9		161.7
Mexican IMMSA Unit
Financial information related to segments
Number of underground poly metal mines | item	5
Mexican IMMSA Unit | Operating segment
Financial information relating to segments
Net sales	$ 704.1	630.8	666.5
Cost of sales (exclusive of depreciation, amortization and depletion)	479.1	545.6	532.8
Selling, general and administrative	12.4	10.4	10.2
Depreciation, amortization and depletion	72.9	70.4	57.6
Exploration	10.5	8.6	5.4
Operating income	129.2	(4.2)	60.6
Capital investment	122.6	147.7	161.8
Property and mine development, net	801.0	751.0	678.5
Total assets	1,204.5	1,166.1	1,100.7
Mexican IMMSA Unit | Reportable subsegments | Operating segment
Financial information relating to segments
Net sales	523.6	479.2	528.5
Mexican IMMSA Unit | Intersegment sales | Operating segment
Financial information relating to segments
Net sales	$ 180.5	151.6	138.0
Peruvian Operations
Financial information related to segments
Number of open-pit copper mines | item	2
Peruvian Operations | Operating segment
Financial information relating to segments
Net sales	$ 4,604.6	3,854.3	3,908.5
Cost of sales (exclusive of depreciation, amortization and depletion)	2,111.4	1,974.7	2,061.3
Selling, general and administrative	38.1	38.4	39.2
Depreciation, amortization and depletion	329.5	338.7	321.7
Exploration	33.2	29.1	18.5
Operating income	2,092.5	1,473.4	1,467.8
Capital investment	271.2	322.7	355.0
Property and mine development, net	3,759.7	3,624.2	3,659.3
Total assets	5,278.3	4,635.5	4,870.8
Peruvian Operations | Reportable subsegments | Operating segment
Financial information relating to segments
Net sales	$ 4,604.6	$ 3,854.3	$ 3,908.5