Derivatives and Fair Value Measurements (Details) In Millions, unless otherwise specified	9 Months Ended												12 Months Ended
	Sep. 30, 2014	Sep. 30, 2014 Interest rate swap [Member] USD ($)	Sep. 30, 2014 Foreign currency forward contract [Member] USD ($)	Sep. 30, 2014 Foreign currency forward contract [Member] AUD	Sep. 30, 2014 Foreign currency forward contract [Member] Cash flow hedges [Member] AUD	Sep. 30, 2014 Foreign currency forward contract [Member] Fair value hedge [Member] AUD	Sep. 30, 2014 Foreign currency forward contract [Member] Economic hedge [Member] AUD	Sep. 30, 2014 Diesel fuel hedge contracts [Member] USD ($) gal	Sep. 30, 2014 Diesel fuel hedge contracts [Member] Cash flow hedges [Member] gal	Sep. 30, 2014 Diesel fuel hedge contracts [Member] Fair value hedge [Member] gal	Sep. 30, 2014 Diesel fuel hedge contracts [Member] Economic hedge [Member] gal	Sep. 30, 2014 Explosives hedge contracts [Member] MMbtu	Sep. 30, 2015 Scenario, Forecast [Member] Foreign currency forward contract [Member] USD ($)	Sep. 30, 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		3,597.4	3,597.4	0	0
2014 (A$ millions)				406.3
2015 (A$ millions)				1,661.1
2016 (A$ millions)				1,007.0
2017 (A$ millions)				523.0
Total (gallons/MMbtu)								181,900,000	181,900,000	0	0	0
2014 (gallons/MMbtu)								25,600,000
2015 (gallons/MMbtu)								85,500,000
2016 (gallons/MMbtu)								53,300,000
2017 (gallons/MMbtu)								17,500,000
Fair Value Net Liability			(315.0)					(28.7)
Net loss to be reclassified from accumulated other comprehensive (loss) income to earnings over the next 12 months													$ 130	$ 20
Timing differences between the hedge settlement and the purchase transaction	Less than a day and up to a maximum of 30 days