Business Segments (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net sales	$ 1,388.9us-gaap_SalesRevenueGoodsNet	$ 2,447.4us-gaap_SalesRevenueGoodsNet
Cost of product sold (exclusive of depreciation and amortization)	1,073.6	2,076.9
Direct operating expenses (exclusive of depreciation and amortization)	111.4us-gaap_DirectOperatingCosts	123.4us-gaap_DirectOperatingCosts
Depreciation and amortization	42.0	37.3
Operating income	136.6us-gaap_OperatingIncomeLoss	183.5us-gaap_OperatingIncomeLoss
Capital expenditures	45.5	61.9
Total assets	3,456.1us-gaap_Assets		3,462.5us-gaap_Assets
Goodwill	41.0us-gaap_Goodwill		41.0us-gaap_Goodwill
Operating Segments \| Petroleum
Segment Reporting Information [Line Items]
Net sales	1,304.4	2,375.3
Cost of product sold (exclusive of depreciation and amortization)	1,056.1	2,063.3
Direct operating expenses (exclusive of depreciation and amortization)	87.0	99.2
Depreciation and amortization	34.0	29.5
Operating income	109.2	164.6
Capital expenditures	41.7	57.9
Total assets	2,419.5		2,417.8
Goodwill	0		0
Operating Segments \| Nitrogen Fertilizer
Segment Reporting Information [Line Items]
Net sales	93.1	80.3
Cost of product sold (exclusive of depreciation and amortization)	25.8	21.7
Direct operating expenses (exclusive of depreciation and amortization)	24.4	24.2
Depreciation and amortization	6.8	6.7
Operating income	31.5	23.1
Capital expenditures	2.7	3.4
Total assets	568.1		578.8
Goodwill	41.0		41.0
Intersegment elimination
Segment Reporting Information [Line Items]
Net sales	(8.6)	(8.2)
Cost of product sold (exclusive of depreciation and amortization)	(8.3)	(8.1)
Other
Segment Reporting Information [Line Items]
Direct operating expenses (exclusive of depreciation and amortization)	0	0
Depreciation and amortization	1.2	1.1
Operating income	(4.1)	(4.2)
Capital expenditures	1.1	0.6
Total assets	468.5		465.9
Goodwill	$ 0		$ 0

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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