Fair Value Measurements - Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Assets:
Derivative assets	$ 191.0	$ 347.2
Liabilities:
Derivative liabilities	155.8	332.5
Transfers from Level 1 to Level 2, assets	0.0	0.0
Transfers from Level 2 to Level 1, assets	0.0	0.0
Transfers from Level 1 to Level 2, liabilities	0.0	0.0
Transfers from Level 2 to Level 1, liabilities	0.0	0.0
Commodity contracts
Assets:
Derivative assets	176.3	331.2
Liabilities:
Derivative liabilities	145.0	326.1
Foreign currency contracts
Assets:
Derivative assets	14.8	16.0
Liabilities:
Derivative liabilities	10.8	6.4
Fair value measured on recurring basis
Assets:
Total assets at fair value	195.4	351.2
Liabilities:
Total liabilities at fair value	155.8	332.5
Fair value measured on recurring basis | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	4.4	4.0
Fair value measured on recurring basis | Commodity contracts
Assets:
Derivative assets	176.3	331.2
Liabilities:
Derivative liabilities	145.0	326.1
Fair value measured on recurring basis | Foreign currency contracts
Assets:
Derivative assets	14.8	16.0
Liabilities:
Derivative liabilities	10.8	6.4
Level 1 Inputs
Assets:
Total assets at fair value	132.0	273.6
Liabilities:
Total liabilities at fair value	104.4	236.6
Level 1 Inputs | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	0.0	0.0
Level 1 Inputs | Commodity contracts
Assets:
Derivative assets	132.0	273.6
Liabilities:
Derivative liabilities	104.4	236.6
Level 1 Inputs | Foreign currency contracts
Assets:
Derivative assets	0.0	0.0
Liabilities:
Derivative liabilities	0.0	0.0
Level 2 Inputs
Assets:
Total assets at fair value	61.9	75.3
Liabilities:
Total liabilities at fair value	51.2	95.2
Level 2 Inputs | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	4.4	4.0
Level 2 Inputs | Commodity contracts
Assets:
Derivative assets	42.7	55.3
Liabilities:
Derivative liabilities	40.3	88.8
Level 2 Inputs | Foreign currency contracts
Assets:
Derivative assets	14.8	16.0
Liabilities:
Derivative liabilities	10.8	6.4
Level 3 Inputs
Assets:
Total assets at fair value	1.5	2.3
Liabilities:
Total liabilities at fair value	0.3	0.7
Level 3 Inputs | Cash surrender value of life insurance
Assets:
Cash surrender value of life insurance	0.0	0.0
Level 3 Inputs | Commodity contracts
Assets:
Derivative assets	1.5	2.3
Liabilities:
Derivative liabilities	0.3	0.7
Level 3 Inputs | Foreign currency contracts
Assets:
Derivative assets	0.0	0.0
Liabilities:
Derivative liabilities	0.0	0.0
Level 3 Inputs | Fair value measured on recurring basis
Assets and liabilities measured at estimated fair value on a recurring basis
Debt	1,100.0	1,200.0
Notes receivable	$ 19.1	$ 16.9