Environmental and Legal Contingencies (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Oct. 17, 2012	Jul. 17, 2014	May 31, 2014
Hamilton Plant [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	$ 0.7
Mansfield Works [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	1.1
Proposed civil penalty related to environmental issue		0.3
Ashland coke plant [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	0.5
Ambridge Works [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	2.1
Dicks Creek [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	16.2
Mountain State Carbon, LLC [Member]
Site Contingency [Line Items]
Proposed civil penalty related to environmental issue			$ 2.4	$ 10.6