Fair Value Measurements - Commodity and Foreign Currency Contracts (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets:
Gross Amounts Recognized	$ 261.1	$ 845.8
Gross Amounts Offset	131.1	647.0
Net Amounts Presented	130.0	198.8
Cash Collateral	0.0	3.0
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	130.0	195.8
Liabilities:
Gross Derivative Liabilities	266.6	769.1
Gross Amounts Offset	131.1	647.0
Net Amounts Presented	135.5	122.2
Cash Collateral	29.3	0.0
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	106.3	122.2
Commodity contracts
Assets:
Gross Amounts Recognized	259.0	841.2
Gross Amounts Offset	130.0	646.0
Net Amounts Presented	129.0	195.1
Cash Collateral	0.0	3.0
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	129.0	192.1
Liabilities:
Gross Derivative Liabilities	255.0	767.9
Gross Amounts Offset	130.0	646.0
Net Amounts Presented	125.0	121.9
Cash Collateral	29.3	0.0
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	95.7	121.9
Foreign currency contracts
Assets:
Gross Amounts Recognized	2.0	4.6
Gross Amounts Offset	1.0	0.9
Net Amounts Presented	1.0	3.7
Cash Collateral	0.0	0.0
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	1.0	3.7
Liabilities:
Gross Derivative Liabilities	11.6	1.2
Gross Amounts Offset	1.0	0.9
Net Amounts Presented	10.5	0.3
Cash Collateral	0.0	0.0
Gross Amounts Without Right of Offset	0.0	0.0
Net Amounts	$ 10.5	$ 0.3