Fair Value Measurements - Assets and Liabilities (Details) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset	[1]	$ 427.8	$ 522.9
Derivative liability	[1]	410.9	468.7
Total, inventories liability			14.3
Level 1
Assets and liabilities measured at estimated fair value on a recurring basis
Subtotal Assets		236.1	255.4
Subtotal Liabilities		279.2	340.1
Level 2
Assets and liabilities measured at estimated fair value on a recurring basis
Subtotal Assets		192.1	266.7
Inventories liability			14.3
Subtotal Liabilities		131.4	142.7
Assets and liabilities measured at estimated fair value on a nonrecurring basis
Fair value of inventory disposal group		4.5
Level 3
Assets and liabilities measured at estimated fair value on a recurring basis
Subtotal Assets		3.0	3.2
Subtotal Liabilities		0.3	0.2
Assets and liabilities measured at estimated fair value on a nonrecurring basis
Fair value of asset disposal group, excluding inventory		34.7
Fair value of liability disposal group		10.6
Cash surrender value of life insurance
Assets and liabilities measured at estimated fair value on a recurring basis
Investments		3.3	2.4
Cash surrender value of life insurance | Level 2
Assets and liabilities measured at estimated fair value on a recurring basis
Investments		3.3	2.4
Fair value measured on recurring basis
Assets and liabilities measured at estimated fair value on a recurring basis
Subtotal Assets		431.1	525.3
Netting and collateral, asset		(286.9)	(283.1)
Total Assets		144.2	242.2
Inventories liability			14.3
Subtotal Liabilities		410.9	483.0
Netting and collateral, liability		(345.9)	(393.7)
Total Liabilities		65.1	89.3
Fair value measured on recurring basis | Level 3
Assets and liabilities measured at estimated fair value on a recurring basis
Debt	[2]	805.2	772.2
Notes receivable		6.1	7.4
Fair value measured on recurring basis | Cash surrender value of life insurance
Assets and liabilities measured at estimated fair value on a recurring basis
Investments		3.3	2.4
Commodity contracts
Assets and liabilities measured at estimated fair value on a recurring basis
Total, derivative asset	[2]	139.5	231.5
Total, derivative liability	[2]	61.3	74.1
Commodity contracts | Level 1
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		236.1	255.4
Derivative liability		279.2	340.1
Commodity contracts | Level 2
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		178.7	251.9
Derivative liability		119.0	123.4
Commodity contracts | Level 3
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		3.0	3.2
Derivative liability		0.3	0.2
Commodity contracts | Fair value measured on recurring basis
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		417.7	510.5
Netting and collateral, derivative asset		(278.2)	(279.0)
Total, derivative asset		139.5	231.5
Derivative liability		398.5	463.7
Netting and collateral, derivative liability		(337.2)	(389.6)
Total, derivative liability		61.3	74.1
Foreign currency contracts
Assets and liabilities measured at estimated fair value on a recurring basis
Total, derivative asset	[2]	1.4	8.3
Total, derivative liability	[2]	3.7	0.9
Foreign currency contracts | Level 2
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		10.1	12.4
Derivative liability		12.4	5.0
Foreign currency contracts | Fair value measured on recurring basis
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		10.1	12.4
Netting and collateral, derivative asset		(8.7)	(4.1)
Total, derivative asset		1.4	8.3
Derivative liability		12.4	5.0
Netting and collateral, derivative liability		(8.7)	(4.1)
Total, derivative liability		$ 3.7	$ 0.9

[1] Amounts may not add due to rounding

[2] Amounts may not add due to rounding