Commitments and Contingencies (Details) CAD in Millions, $ in Millions				1 Months Ended					6 Months Ended		12 Months Ended
	May. 30, 2012 action	Mar. 15, 2012 officer	Jan. 26, 2012 officer	Aug. 31, 2014 property party	Apr. 30, 2014 CAD employee	Sep. 30, 2013 property party	Feb. 29, 2012 complaint	Jun. 30, 2010 issue	Jul. 15, 2015	Jun. 30, 2015 USD ($)	Dec. 31, 2012 property	Apr. 30, 2015 USD ($)
Commitments and contingencies
Disputed Proof of Claim Issues | issue								2
Extension period to submit proposed final order								90 days
Comment letter period										30 days
Accruals for unrecognized tax benefits related to disposition | $										$ 33.0
Number of employees terminated | employee					302
Wolverine Mine Severance Estimate | CAD					CAD 12.0
Length of time to recall employees					24 months
Environmental Matters | Walter Coke, Inc.
Commitments and contingencies
Number of properties that the entity has agreed to remediate											23
Number of other PRP's in which "Offer to Conduct Work" letter was sent to | party				5		4
Number of residential properties whose sampling has been completed by EPA						1,100
Number of properties exceeding Regional Removal Management Levels (RML's)						400
Number of Phase I properties offered to Potentially Responsible Parties PRP's for cleanup						50
Number of Phase II Properties Offered to Other Potentially Responsible Parties for Clean Up				30
EPA costs incurred at 35th Avenue Superfund Site | $												$ 17.0
Securities Class Actions and Shareholder Derivative Actions
Commitments and contingencies
Number of executive directors as defendants | officer		3	3
Number of actions | action	2
Number of complaints | complaint							3
Maximum
Commitments and contingencies
Number of years the state impact of any federal changes remains subject to examination										5 years
Number of years the Company remains subject to income tax in various states for prior periods										11 years
Number of years for which the tax years are typically subject to examination in the major non-U.S. jurisdictions										6 years
Minimum
Commitments and contingencies
Number of years the Company remains subject to income tax in various states for prior periods										3 years
Number of years for which the tax years are typically subject to examination in the major non-U.S. jurisdictions										3 years
Subsequent Event | Securities Class Actions and Shareholder Derivative Actions
Commitments and contingencies
Litigation Settlement, Amount									25.0