Fair Value Measurements - Assets and Liabilities (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Assets and liabilities measured at estimated fair value on a recurring basis
Debt	$ 765,300,000	$ 910,200,000
Assets:
Derivative assets	533,900,000	312,000,000.0
Liabilities:
Derivative liabilities	549,200,000	332,500,000
Transfers from Level 1 to Level 2, assets	0	0
Transfers from Level 2 to Level 1, assets	0	0
Transfers from Level 1 to Level 2, liabilities	0	0
Transfers from Level 2 to Level 1, liabilities	0	0
Commodity contracts
Assets:
Derivative assets	515,000,000.0	303,600,000
Liabilities:
Derivative liabilities	540,400,000	323,900,000
Foreign currency contracts
Assets:
Derivative assets	18,900,000	8,500,000
Liabilities:
Derivative liabilities	8,800,000	8,700,000
Fair value measured on recurring basis
Assets:
Total assets at fair value	540,000,000.0	317,700,000
Liabilities:
Total liabilities at fair value	549,200,000	332,500,000
Fair value measured on recurring basis | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	6,000,000.0	5,600,000
Fair value measured on recurring basis | Commodity contracts
Assets:
Derivative assets	515,000,000.0	303,600,000
Liabilities:
Derivative liabilities	540,400,000	323,900,000
Fair value measured on recurring basis | Foreign currency contracts
Assets:
Derivative assets	18,900,000	8,500,000
Liabilities:
Derivative liabilities	8,800,000	8,700,000
Level 1 Inputs | Fair value measured on recurring basis
Assets:
Total assets at fair value	371,600,000	196,300,000
Liabilities:
Total liabilities at fair value	364,200,000	210,600,000
Level 1 Inputs | Fair value measured on recurring basis | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	0	0
Level 1 Inputs | Fair value measured on recurring basis | Commodity contracts
Assets:
Derivative assets	371,600,000	196,300,000
Liabilities:
Derivative liabilities	364,200,000	210,600,000
Level 1 Inputs | Fair value measured on recurring basis | Foreign currency contracts
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Level 2 Inputs | Fair value measured on recurring basis
Assets and liabilities measured at estimated fair value on a recurring basis
Debt	765,300,000	910,200,000
Notes receivable	26,800,000	44,900,000
Assets:
Total assets at fair value	166,200,000	120,200,000
Liabilities:
Total liabilities at fair value	182,600,000	120,500,000
Level 2 Inputs | Fair value measured on recurring basis | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	6,000,000.0	5,600,000
Level 2 Inputs | Fair value measured on recurring basis | Commodity contracts
Assets:
Derivative assets	141,200,000	106,100,000
Liabilities:
Derivative liabilities	173,800,000	111,800,000
Level 2 Inputs | Fair value measured on recurring basis | Foreign currency contracts
Assets:
Derivative assets	18,900,000	8,500,000
Liabilities:
Derivative liabilities	8,800,000	8,700,000
Level 3 Inputs | Fair value measured on recurring basis
Assets:
Total assets at fair value	2,200,000	1,200,000
Liabilities:
Total liabilities at fair value	2,400,000	1,400,000
Level 3 Inputs | Fair value measured on recurring basis | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	0	0
Level 3 Inputs | Fair value measured on recurring basis | Commodity contracts
Assets:
Derivative assets	2,200,000	1,200,000
Liabilities:
Derivative liabilities	2,400,000	1,400,000
Level 3 Inputs | Fair value measured on recurring basis | Foreign currency contracts
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	$ 0	$ 0