Derivatives and Fair Value Measurements (Details) In Millions, unless otherwise specified	12 Months Ended													12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014 Interest rate swaps [Member] USD ($)	Dec. 31, 2014 Foreign currency forward contracts [Member] USD ($)	Dec. 31, 2014 Foreign currency forward contracts [Member] AUD	Dec. 31, 2014 Foreign currency forward contracts [Member] Cash flow hedges [Member] AUD	Dec. 31, 2014 Foreign currency forward contracts [Member] Fair value hedge [Member] AUD	Dec. 31, 2014 Foreign currency forward contracts [Member] Economic hedge [Member] AUD	Nov. 30, 2012 Foreign currency forward contracts [Member] Previously monetized hedge contracts [Member] AUD	Dec. 31, 2014 Diesel fuel hedge contracts [Member] USD ($) gal	Dec. 31, 2014 Diesel fuel hedge contracts [Member] Cash flow hedges [Member] gal	Dec. 31, 2014 Diesel fuel hedge contracts [Member] Fair value hedge [Member] gal	Dec. 31, 2014 Diesel fuel hedge contracts [Member] Economic hedge [Member] gal	Dec. 31, 2014 Explosives hedge contracts [Member] MMbtu	Dec. 31, 2015 Scenario, Forecast [Member] Foreign currency forward contracts [Member] USD ($)	Dec. 31, 2015 Scenario, Forecast [Member] Diesel fuel hedge contracts [Member] USD ($)
Company's foreign currency and commodity positions by Year of Maturity and Account Classification
Total (A$ millions)		$ 0		3,191.1	3,191.1	0	0	1,900.0
2015 (A$ millions)				1,661.1
2016 (A$ millions)				1,007.0
2017 (A$ millions)				523.0
Total (gallons/MMbtu)									201,500,000	201,500,000	0	0	0
2015 (gallons)									103,400,000
2016 (gallons)									67,500,000
2017 (gallons)									30,600,000
Fair Value Net Liability			(410.0)						(167.1)
Net loss to be reclassified from accumulated other comprehensive loss to earnings over the next 12 months														$ 226	$ 100
Timing differences between the hedge settlement and the purchase transaction	Less than a day and up to a maximum of 30 days