REVENUE: - Revenue by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue Recognition
Net sales	$ 2,897.0	$ 1,785.4	$ 5,429.5	$ 3,505.1
Corporate, other and eliminations
Revenue Recognition
Net sales	(38.8)	(21.5)	(65.0)	(48.3)
Mexican Open-pit \| Operating segment
Revenue Recognition
Net sales	1,632.2	1,016.7	3,110.7	1,970.4
Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	161.4	101.6	285.7	236.1
Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	1,142.2	688.6	2,098.1	1,346.9
Copper
Revenue Recognition
Net sales	2,348.2	1,469.7	4,465.6	2,835.5
Copper \| Corporate, other and eliminations
Revenue Recognition
Net sales	(19.2)	(7.7)	(32.9)	(20.6)
Copper \| Mexican Open-pit \| Operating segment
Revenue Recognition
Net sales	1,382.6	866.0	2,663.1	1,665.7
Copper \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	27.4	11.7	51.2	29.7
Copper \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	957.4	599.7	1,784.2	1,160.7
Molybdenum
Revenue Recognition
Net sales	282.2	107.0	451.8	233.0
Molybdenum \| Mexican Open-pit \| Operating segment
Revenue Recognition
Net sales	149.6	58.1	240.7	130.1
Molybdenum \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	132.6	48.9	211.1	102.9
Silver
Revenue Recognition
Net sales	120.2	48.4	259.2	113.2
Silver \| Corporate, other and eliminations
Revenue Recognition
Net sales	(17.4)	(2.8)	(29.1)	(3.3)
Silver \| Mexican Open-pit \| Operating segment
Revenue Recognition
Net sales	68.0		140.7
Silver \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	36.9	51.2	85.4	116.5
Silver \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	32.7		62.2
Zinc
Revenue Recognition
Net sales	81.3	99.2	117.0	187.4
Zinc \| Corporate, other and eliminations
Revenue Recognition
Net sales		(9.5)	0.5	(21.4)
Zinc \| Mexican Open-pit \| Operating segment
Revenue Recognition
Net sales		59.0		103.6
Zinc \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	81.3	27.2	116.5	62.7
Zinc \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales		22.5		42.5
Other
Revenue Recognition
Net sales	65.1	61.1	135.9	136.0
Other \| Corporate, other and eliminations
Revenue Recognition
Net sales	(2.2)	(1.5)	(3.5)	(3.0)
Other \| Mexican Open-pit \| Operating segment
Revenue Recognition
Net sales	32.0	33.6	66.2	71.0
Other \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	15.8	11.5	32.6	27.2
Other \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	$ 19.5	$ 17.5	$ 40.6	$ 40.8