Fair Value Measurements - Assets and Liabilities (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Assets and liabilities measured at estimated fair value on a recurring basis
Debt	$ 1,151,700,000	$ 1,186,300,000
Assets:
Derivative assets	261,800,000	347,200,000
Liabilities:
Derivative liabilities	251,900,000	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	256,800,000	331,200,000
Liabilities:
Derivative liabilities	242,400,000	326,100,000
Foreign currency contracts
Assets:
Derivative assets	5,000,000.0	16,000,000.0
Liabilities:
Derivative liabilities	9,500,000	6,400,000
Fair value measured on recurring basis
Assets:
Total assets at fair value	267,200,000	351,200,000
Liabilities:
Total liabilities at fair value	251,900,000	332,500,000
Fair value measured on recurring basis | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	5,400,000	4,000,000.0
Fair value measured on recurring basis | Commodity contracts
Assets:
Derivative assets	256,800,000	331,200,000
Liabilities:
Derivative liabilities	242,400,000	326,100,000
Fair value measured on recurring basis | Foreign currency contracts
Assets:
Derivative assets	5,000,000.0	16,000,000.0
Liabilities:
Derivative liabilities	9,500,000	6,400,000
Level 1 Inputs | Fair value measured on recurring basis
Assets:
Total assets at fair value	208,700,000	273,600,000
Liabilities:
Total liabilities at fair value	187,300,000	236,600,000
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	208,700,000	273,600,000
Liabilities:
Derivative liabilities	187,300,000	236,600,000
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:
Total assets at fair value	57,100,000	75,300,000
Liabilities:
Total liabilities at fair value	64,300,000	95,200,000
Level 2 Inputs | Fair value measured on recurring basis | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	5,400,000	4,000,000.0
Level 2 Inputs | Fair value measured on recurring basis | Commodity contracts
Assets:
Derivative assets	46,700,000	55,300,000
Liabilities:
Derivative liabilities	54,800,000	88,800,000
Level 2 Inputs | Fair value measured on recurring basis | Foreign currency contracts
Assets:
Derivative assets	5,000,000.0	16,000,000.0
Liabilities:
Derivative liabilities	9,500,000	6,400,000
Level 3 Inputs | Fair value measured on recurring basis
Assets and liabilities measured at estimated fair value on a recurring basis
Debt	1,200,000,000	1,200,000,000
Notes receivable	65,400,000	16,900,000
Assets:
Total assets at fair value	1,400,000	2,300,000
Liabilities:
Total liabilities at fair value	200,000	700,000
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	1,400,000	2,300,000
Liabilities:
Derivative liabilities	200,000	700,000
Level 3 Inputs | Fair value measured on recurring basis | Foreign currency contracts
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	$ 0	$ 0