Commitments and Contingencies (Details 2) AUD in Millions, $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2017 USD ($) sites	Mar. 31, 2017 AUD sites	Dec. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Oct. 07, 2016 USD ($)
Loss Contingency [Abstract]
Senior Notes					$ 287.0
Monto Coal Pty Limited [Member]
Loss Contingency [Abstract]
Ownership percentage in subsidiaries	51.00%
Loss Contingency Damages Sought Minimum | AUD		AUD 15.6
Loss Contingency Damages Sought Value Max | AUD		AUD 1,800.0
Gold Fields [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	4	4
Undiscounted environmental clean-up liabilities, total	$ 62.8
Senior Notes [Member]
Loss Contingency [Abstract]
Debt Instrument, Face Amount	1,650.0
Berenergy [Member]
Loss Contingency [Abstract]
Litigation Settlement Damages Awarded to Plaintiff	0.9
Loss Contingency Accrual	13.1
Bankruptcy unliquidated, general unsecured claim [Member] | Blue Tee [Member]
Loss Contingency [Abstract]
Bankruptcy Claims, Amount of Claims Filed	65.6
Bankruptcy additional unliquidated, in an unknown amount [Member] | Blue Tee [Member]
Loss Contingency [Abstract]
Bankruptcy Claims, Amount of Claims Filed	150.0
Bankruptcy further contingent claims, at known and unknown sites [Member] | Blue Tee [Member]
Loss Contingency [Abstract]
Bankruptcy Claims, Amount of Claims Filed	$ 500.0
Bankruptcy unliquidated, secured and general unsecured [Member] | Gold Fields [Member]
Loss Contingency [Abstract]
Bankruptcy Claims, Amount of Claims Filed			$ 1,200.0	$ 2,700.0