XML 135 R114.htm IDEA: XBRL DOCUMENT v3.8.0.1
Asset Retirement Obligations (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2017
Apr. 01, 2017
Jun. 30, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]            
Surety bonds and bank guarantees outstanding to secure reclamation obligations or activities $ 1,136.8     $ 1,136.8 $ 374.3  
Amount of reclamation self-bonding in certain states in which the company qualifies         1,094.2  
Letters of credit in support of reclamation obligations or activities 188.5     188.5 80.0  
Predecessor            
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]            
Total asset retirement obligation   $ 664.2     758.8 $ 712.1
Current portion   31.1     41.0  
Liabilities settled or disposed   (2.7)     (41.5)  
Accretion expense   12.5     45.7  
Revision to estimates   (104.4)     42.5  
Noncurrent obligation   633.1     717.8  
Balance at end of period — active locations   540.1     634.8  
Balance at end of period — closed or inactive locations   124.1     124.0  
Net gain on disposal of assets   $ (22.8) $ (13.7)   (23.2) $ (45.0)
Credit adjusted, risk-free interest rates           50.83%
Cash collateral in support of reclamation obligations or activities         $ 233.2  
Predecessor | U.S. Obligations [Member]            
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]            
Credit adjusted, risk-free interest rates   9.36%     13.45%  
Predecessor | Australian Operations [Member]            
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]            
Credit adjusted, risk-free interest rates   4.36%     4.92%  
Successor            
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]            
Total asset retirement obligation 691.1 $ 664.2   691.1    
Current portion 34.1     34.1    
Liabilities settled or disposed       (65.2)    
Accretion expense       32.6    
Revision to estimates       59.5    
Noncurrent obligation 657.0     657.0    
Balance at end of period — active locations 612.9     612.9    
Balance at end of period — closed or inactive locations 78.2     78.2    
Net gain on disposal of assets (83.1)     (84.0)    
Cash collateral in support of reclamation obligations or activities $ 205.2     $ 205.2    
Successor | U.S. Obligations [Member]            
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]            
Credit adjusted, risk-free interest rates 9.71%     9.71%    
Successor | Australian Operations [Member]            
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]            
Credit adjusted, risk-free interest rates 4.65%     4.65%