Fair Value Measurements - Commodity and Foreign Currency Contracts (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Assets:
Gross Amounts Recognized	$ 347.2	$ 529.6
Gross Amounts Offset	254.8	261.3
Net Amounts Presented	92.4	268.4
Cash Collateral	27.1	28.4
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	65.3	240.0
Liabilities:
Gross Amounts Recognized	332.5	468.5
Gross Amounts Offset	254.8	261.3
Net Amounts Presented	77.7	207.2
Cash Collateral	2.0	140.8
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	75.7	66.4
Commodity contracts
Assets:
Gross Amounts Recognized	331.2	517.3
Gross Amounts Offset	249.7	257.2
Net Amounts Presented	81.5	260.1
Cash Collateral	27.1	28.4
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	54.5	231.7
Liabilities:
Gross Amounts Recognized	326.1	463.4
Gross Amounts Offset	249.7	257.2
Net Amounts Presented	76.5	206.3
Cash Collateral	2.0	140.8
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	74.5	65.5
Foreign currency contracts
Assets:
Gross Amounts Recognized	16.0	12.4
Gross Amounts Offset	5.1	4.1
Net Amounts Presented	10.9	8.2
Cash Collateral	0.0	0.0
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	10.9	8.2
Liabilities:
Gross Amounts Recognized	6.4	5.0
Gross Amounts Offset	5.1	4.1
Net Amounts Presented	1.2	0.9
Cash Collateral	0.0	0.0
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	$ 1.2	$ 0.9