Fair Value Measurements - Assets and Liabilities (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset	[1]	$ 355.1	$ 522.9
Derivative liability	[1]	348.3	468.7
Total, inventories liability			14.3
Level 1
Assets and liabilities measured at estimated fair value on a recurring basis
Subtotal Assets		213.6	255.4
Subtotal Liabilities		220.9	340.1
Level 2
Assets and liabilities measured at estimated fair value on a recurring basis
Subtotal Assets		144.3	266.7
Inventories liability			14.3
Subtotal Liabilities		127.1	142.7
Level 3
Assets and liabilities measured at estimated fair value on a recurring basis
Subtotal Assets		0.5	3.2
Subtotal Liabilities		0.3	0.2
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		358.4	525.3
Netting and collateral, asset		(296.5)	(283.1)
Total Assets		61.9	242.2
Inventories liability			14.3
Subtotal Liabilities		348.3	483.0
Netting and collateral, liability		(304.7)	(393.7)
Total Liabilities		43.6	89.3
Fair value measured on recurring basis | Level 3
Assets and liabilities measured at estimated fair value on a recurring basis
Debt	[2]	796.5	772.2
Notes receivable		7.4	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]	50.1	231.5
Total, derivative liability	[2]	41.7	74.1
Commodity contracts | Level 1
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		213.6	255.4
Derivative liability		220.9	340.1
Commodity contracts | Level 2
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		123.6	251.9
Derivative liability		116.3	123.4
Commodity contracts | Level 3
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		0.5	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		337.7	510.5
Netting and collateral, derivative asset		(287.6)	(279.0)
Total, derivative asset		50.1	231.5
Derivative liability		337.5	463.7
Netting and collateral, derivative liability		(295.8)	(389.6)
Total, derivative liability		41.7	74.1
Foreign currency contracts
Assets and liabilities measured at estimated fair value on a recurring basis
Total, derivative asset	[2]	8.5	8.3
Total, derivative liability	[2]	1.8	0.9
Foreign currency contracts | Level 2
Assets and liabilities measured at estimated fair value on a recurring basis
Derivative asset		17.4	12.4
Derivative liability		10.8	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		17.4	12.4
Netting and collateral, derivative asset		(8.9)	(4.1)
Total, derivative asset		8.5	8.3
Derivative liability		10.8	5.0
Netting and collateral, derivative liability		(8.9)	(4.1)
Total, derivative liability		$ 1.9	$ 0.9

[1] Amounts may not add due to rounding

[2] Amounts may not add due to rounding