REVENUE: - Revenue by Geographical Areas (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Revenue Recognition
Net sales	$ 2,156.9	$ 2,680.9	$ 7,227.6	$ 8,110.4
Corporate, other and eliminations
Revenue Recognition
Net sales	(19.5)	(42.8)	(281.5)	(107.9)
Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	1,201.5	1,425.8	4,184.7	4,536.6
Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	159.2	175.1	503.0	460.8
Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	815.7	1,122.8	2,821.4	3,220.9
Mexico
Revenue Recognition
Net sales	487.6	560.5	1,632.7	1,620.1
Mexico \| Corporate, other and eliminations
Revenue Recognition
Net sales	(30.9)	(42.8)	(114.9)	(107.9)
Mexico \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	414.7	483.1	1,390.8	1,431.7
Mexico \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	103.8	115.7	356.8	291.8
Mexico \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales		4.5		4.5
United States
Revenue Recognition
Net sales	431.7	407.4	1,557.3	1,302.6
United States \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	333.9	324.9	1,237.2	1,107.5
United States \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	11.4	11.2	37.8	42.9
United States \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	86.4	71.3	282.3	152.2
Peru
Revenue Recognition
Net sales	118.3	147.9	451.6	438.6
Peru \| Corporate, other and eliminations
Revenue Recognition
Net sales	11.4		(166.6)
Peru \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	(19.7)		158.6
Peru \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales		(0.4)		(0.3)
Peru \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	126.6	148.3	459.6	438.9
Brazil
Revenue Recognition
Net sales	120.6	104.1	345.0	329.2
Brazil \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	16.1	10.9	25.7	18.4
Brazil \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	104.5	93.2	319.3	310.8
Chile
Revenue Recognition
Net sales	101.6	113.7	287.1	267.9
Chile \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	10.4	(0.1)	10.9	2.8
Chile \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	91.2	113.8	276.2	265.1
Other American countries
Revenue Recognition
Net sales	19.7	12.7	53.0	34.2
Other American countries \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	10.8	10.9	28.5	28.9
Other American countries \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	1.2		2.2	0.7
Other American countries \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	7.7	1.8	22.3	4.6
Switzerland
Revenue Recognition
Net sales	296.4	423.9	1,001.8	1,257.8
Switzerland \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	123.9	276.0	450.2	888.7
Switzerland \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	10.9	20.3	33.8	46.0
Switzerland \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	161.6	127.6	517.8	323.1
Italy
Revenue Recognition
Net sales	80.5	66.8	211.7	250.9
Italy \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales			1.3	0.2
Italy \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	6.2	3.9	13.9	5.9
Italy \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	74.3	62.9	196.5	244.8
Spain
Revenue Recognition
Net sales	87.2	127.0	327.3	363.6
Spain \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	90.2	106.6	290.5	299.8
Spain \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	(3.0)	20.4	36.8	63.8
Other European Countries
Revenue Recognition
Net sales	101.5	172.1	258.0	553.3
Other European Countries \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	49.0	54.2	90.9	202.2
Other European Countries \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	9.6	7.0	24.0	40.3
Other European Countries \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	42.9	110.9	143.1	310.8
China
Revenue Recognition
Net sales	120.0	21.5	326.9	150.0
China \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	101.9	21.3	308.8	125.0
China \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	18.1	0.2	18.1	25.0
Singapore
Revenue Recognition
Net sales	62.1	285.9	161.0	765.3
Singapore \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	48.1	119.9	53.5	354.8
Singapore \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	(0.1)	6.3	8.4	14.8
Singapore \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	14.1	159.7	99.1	395.7
Japan
Revenue Recognition
Net sales	93.8	166.9	431.4	501.7
Japan \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	9.2	(0.8)	51.8	23.6
Japan \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	84.6	167.7	379.6	478.1
Other Asian countries
Revenue Recognition
Net sales	35.9	70.5	182.8	275.2
Other Asian countries \| Mexican Open-Pit \| Operating segment
Revenue Recognition
Net sales	29.1	29.8	111.7	71.4
Other Asian countries \| Mexican IMMSA Unit \| Operating segment
Revenue Recognition
Net sales	0.1	0.2	0.4	0.3
Other Asian countries \| Peruvian Operations \| Operating segment
Revenue Recognition
Net sales	$ 6.7	$ 40.5	$ 70.7	$ 203.5