Fair Value Measurements - Commodity and Foreign Currency Contracts (Details) - USD ($)
$ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
| Offsetting Assets [Line Items] |
|
|
| Gross Amounts Recognized |
$ 315.5
|
$ 312.0
|
| Gross Amounts Offset |
245.8
|
235.2
|
| Net Amounts Presented |
69.7
|
76.9
|
| Cash Collateral |
0.0
|
21.2
|
| Gross Amounts without Right of Offset |
0.0
|
0.0
|
| Net Amounts |
69.7
|
55.7
|
| Offsetting Liabilities [Line Items] |
|
|
| Gross Amounts Recognized |
320.1
|
332.5
|
| Gross Amounts Offset |
245.8
|
235.2
|
| Net Amounts Presented |
74.3
|
97.4
|
| Cash Collateral |
7.9
|
39.2
|
| Gross Amounts without Right of Offset |
0.0
|
0.0
|
| Net Amounts |
66.4
|
58.2
|
| Commodity contracts |
|
|
| Offsetting Assets [Line Items] |
|
|
| Gross Amounts Recognized |
308.0
|
303.6
|
| Gross Amounts Offset |
239.4
|
228.4
|
| Net Amounts Presented |
68.6
|
75.1
|
| Cash Collateral |
0.0
|
21.2
|
| Gross Amounts without Right of Offset |
0.0
|
0.0
|
| Net Amounts |
68.6
|
53.9
|
| Offsetting Liabilities [Line Items] |
|
|
| Gross Amounts Recognized |
307.0
|
323.9
|
| Gross Amounts Offset |
239.4
|
228.4
|
| Net Amounts Presented |
67.6
|
95.4
|
| Cash Collateral |
7.9
|
39.2
|
| Gross Amounts without Right of Offset |
0.0
|
0.0
|
| Net Amounts |
59.7
|
56.2
|
| Foreign currency contracts |
|
|
| Offsetting Assets [Line Items] |
|
|
| Gross Amounts Recognized |
7.5
|
8.5
|
| Gross Amounts Offset |
6.4
|
6.7
|
| Net Amounts Presented |
1.1
|
1.7
|
| Cash Collateral |
0.0
|
0.0
|
| Gross Amounts without Right of Offset |
0.0
|
0.0
|
| Net Amounts |
1.1
|
1.7
|
| Offsetting Liabilities [Line Items] |
|
|
| Gross Amounts Recognized |
13.2
|
8.7
|
| Gross Amounts Offset |
6.4
|
6.7
|
| Net Amounts Presented |
6.8
|
2.0
|
| Cash Collateral |
0.0
|
0.0
|
| Gross Amounts without Right of Offset |
0.0
|
0.0
|
| Net Amounts |
$ 6.8
|
$ 2.0
|