Fair Value Measurements - Level 3 Inputs (Details) - Commodity contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Revenue
Change in fair value of assets and liabilities measured on recurring basis, utilized Level 3 inputs
Beginning of Period	$ 4.2
Total Gains (Losses) Included in Earnings	3.4	$ 12.7
Settlements	5.3	8.9
Transfers into Level 3	1.0	0.4
End of Period	3.3	4.2
Change in Unrealized Gains Relating to Assets (Liabilities) that are Held at end of Period	2.8	4.2
Cost of revenue.
Change in fair value of assets and liabilities measured on recurring basis, utilized Level 3 inputs
Beginning of Period	1.3
Total Gains (Losses) Included in Earnings	0.6	(1.4)
Settlements	0.5	0.1
Transfers into Level 3	(0.1)
End of Period	0.3	1.3
Change in Unrealized Gains Relating to Assets (Liabilities) that are Held at end of Period	$ 0.2	$ (1.3)