Derivatives and Fair Value Measurements (Details) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended						12 Months Ended					12 Months Ended
	Mar. 31, 2014	Mar. 31, 2014 Interest Rate Swap [Member] USD ($)	Mar. 31, 2015 Foreign Currency Forward Contract [Member] USD ($)	Mar. 31, 2014 Foreign Currency Forward Contract [Member] USD ($)	Mar. 31, 2014 Foreign Currency Forward Contract [Member] AUD	Mar. 31, 2014 Foreign Currency Forward Contract [Member] Fair value hedge [Member] AUD	Mar. 31, 2014 Foreign Currency Forward Contract [Member] Cash flow hedges [Member] AUD	Mar. 31, 2014 Foreign Currency Forward Contract [Member] Economic hedge [Member] AUD	Mar. 31, 2015 Diesel fuel hedge contracts [Member] USD ($)	Mar. 31, 2014 Diesel fuel hedge contracts [Member] USD ($) gal	Mar. 31, 2014 Diesel fuel hedge contracts [Member] Fair value hedge [Member] gal	Mar. 31, 2014 Diesel fuel hedge contracts [Member] Cash flow hedges [Member] gal	Mar. 31, 2014 Diesel fuel hedge contracts [Member] Economic hedge [Member] gal	Mar. 31, 2015 Explosives Hedge Contracts Member USD ($)	Mar. 31, 2014 Explosives Hedge Contracts Member USD ($) MMbtu	Mar. 31, 2014 Explosives Hedge Contracts Member Fair value hedge [Member] MMbtu	Mar. 31, 2014 Explosives Hedge Contracts Member Cash flow hedges [Member] MMbtu	Mar. 31, 2014 Explosives Hedge Contracts Member Economic hedge [Member] MMbtu
Company's foreign currency and commodity positions by Year of Maturity and Account Classification
Total (A$ millions)		$ 0			4,630.4	0	4,630.4	0
2014 (A$ millions)					1,501.3
2015 (A$ millions)					1,645.1
2016 (A$ millions)					997.0
2017 (A$ millions)					487.0
Total (gallons/MMbtu)										200,500,000	0	200,500,000	0		800,000	0	800,000	0
2014 (gallons/MMbtu)										79,000,000					800,000
2015 (gallons/MMbtu)										74,200,000					0
2016 (gallons/MMbtu)										42,000,000					0
2017 (gallons/MMbtu)										5,300,000					0
Fair Value Liability				(238.0)						(0.5)					(0.5)
Timing differences between the hedge settlement and the purchase transaction	Less than a day and up to a maximum of 30 days
Gains (losses) to be reclassified from accumulated other comprehensive (loss) income to earnings over the next 12 months			$ (13.0)						$ 0.1					$ (0.5)