Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair values of derivatives on consolidated balance sheets
Other current assets	$ 27.0	$ 72.7
Other noncurrent assets		1.6
Asset Derivative	27.0	74.3
Other current liabilities	(23.3)	(0.2)
Liability derivative	(23.3)	(0.2)
Derivatives not designated as cash flow hedges
Fair values of derivatives on consolidated balance sheets
Asset Derivative	27.0	74.3
Liability derivative	(23.3)	(0.2)
Foreign exchange contracts | Derivatives not designated as cash flow hedges
Fair values of derivatives on consolidated balance sheets
Other current assets		27.3
Other noncurrent assets		1.6
Other current liabilities	(18.5)
Natural gas derivatives | Derivatives not designated as cash flow hedges
Fair values of derivatives on consolidated balance sheets
Other current assets	27.0	45.4
Other current liabilities	$ (4.8)	$ (0.2)