Business Segments (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net sales	$ 2,540.3	$ 2,220.3	$ 4,987.8	$ 4,572.7
Cost of product sold (exclusive of depreciation and amortization)	2,189.0	1,785.4	4,265.9	3,599.0
Direct operating expenses (exclusive of depreciation and amortization)	120.1	108.3	243.5	216.8
Depreciation and amortization	38.6	35.0	75.9	69.2
Operating income	164.6	262.7	348.1	630.3
Capital expenditures	53.0	50.9	114.9	114.6
Total assets	3,979.5		3,979.5		3,665.8
Goodwill	41.0		41.0		41.0
Operating Segments | Petroleum
Segment Reporting Information [Line Items]
Net sales	2,466.3	2,138.1	4,841.7	4,412.1
Cost of product sold (exclusive of depreciation and amortization)	2,172.6	1,776.6	4,236.0	3,582.3
Direct operating expenses (exclusive of depreciation and amortization)	93.2	83.8	192.4	169.9
Depreciation and amortization	30.7	28.4	60.2	56.4
Operating income	151.9	229.1	316.5	564.7
Capital expenditures	47.4	35.5	105.3	80.1
Total assets	2,785.3		2,785.3		2,533.3
Goodwill	0		0		0
Operating Segments | Nitrogen Fertilizer
Segment Reporting Information [Line Items]
Net sales	77.2	88.8	157.5	170.2
Cost of product sold (exclusive of depreciation and amortization)	19.4	15.6	41.1	26.2
Direct operating expenses (exclusive of depreciation and amortization)	26.9	24.4	51.1	47.0
Depreciation and amortization	6.8	6.2	13.5	12.0
Operating income	18.8	37.1	41.9	73.9
Capital expenditures	4.1	13.8	7.5	31.9
Total assets	575.2		575.2		593.5
Goodwill	41.0		41.0		41.0
Intersegment elimination
Segment Reporting Information [Line Items]
Net sales	(3.2)	(6.6)	(11.4)	(9.6)
Cost of product sold (exclusive of depreciation and amortization)	(3.0)	(6.8)	(11.2)	(9.5)
Other
Segment Reporting Information [Line Items]
Direct operating expenses (exclusive of depreciation and amortization)	0	0.1	0	(0.1)
Depreciation and amortization	1.1	0.4	2.2	0.8
Operating income	(6.1)	(3.5)	(10.3)	(8.3)
Capital expenditures	1.5	1.6	2.1	2.6
Total assets	619.0		619.0		539.0
Goodwill	$ 0		$ 0		$ 0