Fair Value Measurements - Commodity and Foreign Currency Contracts (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Offsetting Assets [Line Items]
Gross Amounts Recognized	$ 261.8	$ 347.2
Gross Amounts Offset	203.7	254.8
Net Amounts Presented	58.1	92.4
Cash Collateral	22.4	27.1
Gross Amounts without Right of Offset	0.0	0.0
Net Amounts	35.7	65.3
Offsetting Liabilities [Line Items]
Gross Amounts Recognized	251.9	332.5
Gross Amounts Offset	203.7	254.8
Net Amounts Presented	48.2	77.7
Cash Collateral	11.3	2.0
Gross Amounts without Right of Offset	0.0	0.0
Net Amounts	36.9	75.7
Commodity contracts
Offsetting Assets [Line Items]
Gross Amounts Recognized	256.8	331.2
Gross Amounts Offset	198.9	249.7
Net Amounts Presented	57.9	81.5
Cash Collateral	22.4	27.1
Gross Amounts without Right of Offset	0.0	0.0
Net Amounts	35.5	54.5
Offsetting Liabilities [Line Items]
Gross Amounts Recognized	242.4	326.1
Gross Amounts Offset	198.9	249.7
Net Amounts Presented	43.5	76.5
Cash Collateral	11.3	2.0
Gross Amounts without Right of Offset	0.0	0.0
Net Amounts	32.2	74.5
Foreign currency contracts
Offsetting Assets [Line Items]
Gross Amounts Recognized	5.0	16.0
Gross Amounts Offset	4.8	5.1
Net Amounts Presented	0.2	10.9
Cash Collateral	0.0	0.0
Gross Amounts without Right of Offset	0.0	0.0
Net Amounts	0.2	10.9
Offsetting Liabilities [Line Items]
Gross Amounts Recognized	9.5	6.4
Gross Amounts Offset	4.8	5.1
Net Amounts Presented	4.7	1.2
Cash Collateral	0.0	0.0
Gross Amounts without Right of Offset	0.0	0.0
Net Amounts	$ 4.7	$ 1.2