Union Contracts (Details)	Mar. 31, 2018 employees
Middletown Works [Member]
Concentration Risk [Line Items]
Entity Number of Employees	1,730
Ashland Works [Member]
Concentration Risk [Line Items]
Entity Number of Employees	280
Mountain State Carbon [Member]
Concentration Risk [Line Items]
Entity Number of Employees	200
Butler Works [Member]
Concentration Risk [Line Items]
Entity Number of Employees	1,160

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_ConcentrationRiskLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration