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Group statement of changes in equity (Parenthetical) - USD ($)
$ in Millions
Sep. 01, 2017
Feb. 03, 2016
Coal & Allied Industries Limited [member]    
Additional ownership percentage acquired in subsidiary   20.00%
Ownership percentage in subsidiary   100.00%
Ownership interest in subsidiary sold 100.00%  
Hunter valley operations [member]    
Percentage of ownership interest exchanged in joint venture   32.40%