Contingencies (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 1997	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2008	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			$ 746,000,000	$ 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