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COMMITMENTS AND CONTINGENCIES - Environmental Matters by Site (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Jun. 05, 2007
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2012
Loss contingencies                
Reclamation and remediation   $ 10.0 $ 5.0 $ 55.0 $ 21.0      
Environmental remediation obligations   466.0 $ 285.0 466.0 $ 285.0 $ 279.0 $ 304.0  
Midnite Mine And Dawn Mill Sites [Member]                
Loss contingencies                
Environmental remediation obligations   $ 164.0   $ 164.0        
Midnite Mine                
Loss contingencies                
Department of Interior contribution for past and future cleanup costs               $ 42.0
Environmental remediation | Ross-Adams Mine Site                
Loss contingencies                
Damages sought $ 0.3              
Newmont USA                
Loss contingencies                
Percent ownership held by Newmont   100.00%   100.00%        
Dawn Mining Company                
Loss contingencies                
Percent ownership held by Newmont   51.00%   51.00%