Contingencies (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) claims	Jun. 30, 2013 claims	Dec. 31, 1997	Dec. 31, 2015 USD ($)	Sep. 30, 2008 USD ($)	Dec. 31, 1993
Loss Contingencies [Line Items]
Investment in Trojan						87.00%
Refund to customers for Trojan Investment including interest					$ 33,000,000
Class action damages sought	$ 260,000,000
Site Contingency, Names of Other Potentially Responsible Parties	100		69
Remediation cost estimate lower range	$ 800,000,000
Remediation cost estimate upper range	2,400,000,000			$ 1,500,000,000
Civil Penalty Claim - Per day per violation through January 12, 2009	32,500
Civil Penalty Claim - Per day per violation after January 12, 2009	$ 37,500
Loss Contingency, Actions Taken by Defendant		36
projects added to plaintiff's suit | claims	2
Loss Contingency, Pending Claims, Number | claims	40	39