Commitments and Contingencies (Details 2) T in Millions, AUD in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) mW sites	Dec. 31, 2015 AUD mW sites	Dec. 31, 2014 USD ($) T	Dec. 31, 2013 USD ($)	Jan. 31, 2016	Jan. 19, 2012 USD ($)	Sep. 30, 2011 USD ($)	Dec. 31, 2007 T
Loss Contingency [Abstract]
Additional charge recorded as a result of the damages awarded to Eagle in arbitration	$ (10.6)	$ (15.6)	$ 15.6
Tons Shipped Subject To Contract Pricing Arbitration | T					4.8
Pricing rebate provided in settlement of contract pricing arbitration					$ 68.7
Undiscounted environmental clean-up liabilities, current			$ 23.9		19.4
Gulf Power Company Litigation [Member]
Loss Contingency [Abstract]
Alleged shortage of past and future coal shipments under a coal supply agreement, tons | T										5.0
Litigation Settlement Damages Awarded to Plaintiff									$ 20.6
Litigation Settlement, Prejudgement Interest								$ 6.9
Charge recorded for settlement damages						$ 20.6
Charge recorded for prejudgement interest						$ 6.9
Oklahoma Lead Litigation [Member]
Loss Contingency [Abstract]
Number of national priority list sites based on the Superfund Amendments and Reauthorization Act of 1986 at which Gold Fields or the former affiliate, has been named a potentially responsible party (PRP) | sites			6	6
Number of additional national priority list sites in which claims were asserted | sites			13	13
Total number of national priority list sites | sites			19	19
Reduced number of national priority list sites due to completion of work, transfer or regulatory inactivity | sites			7	7
Undiscounted environmental clean-up liabilities, total			$ 66.9		69.4
Undiscounted environmental clean-up liabilities, current			$ 23.9		19.4
Monto Coal Pty Limited [Member]
Loss Contingency [Abstract]
Ownership Percentage In Subsidiaries			51.00%
Damages sought | AUD				AUD 15.6
Loss contingency damages sought value max | AUD				1,800.0
Eagle Mining [Member]
Loss Contingencies [Line Items]
Gain Related to Litigation Settlement			$ 10.8
Loss Contingency [Abstract]
Loss Contingency Accrual					$ 23.4
Wilkie Creek [Member]
Loss Contingency [Abstract]
Damages sought | AUD				113.1
Potential annual payments awarded | AUD				11.8
PaymentAwarded | AUD				AUD 11.8
Loss Contingency, Loss in Period			$ 9.7
Prarie State Energy Campus [Member]
Loss Contingency [Abstract]
Capacity Of New Electricity Generation Project | mW			1,600	1,600
Undivided Interest Percent Of New Electricity Generation Project			5.06%				5.06%