Segment Disclosures (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012 segment	Mar. 31, 2011	Dec. 31, 2011
Segment Disclosures
Number of business segments	2
Segment data
Net sales	$ 1,527.6	$ 1,174.0
Cost of sales	815.8	649.0
Gross margin	711.8	525.0
Total other operating costs and expenses	56.1	2.1
Equity in earnings of operating affiliates	15.5	11.5
Operating earnings	671.2	534.4
Assets	9,616.9		8,974.5
Ammonia
Segment data
Net sales	401.7	202.5
Granular urea
Segment data
Net sales	349.4	224.3
UAN
Segment data
Net sales	423.7	402.3
AN
Segment data
Net sales	63.8	61.3
DAP
Segment data
Net sales	209.3	186.0
MAP
Segment data
Net sales	46.6	62.1
All Other
Segment data
Net sales	33.1	35.5
Nitrogen
Segment data
Net sales	1,271.7	925.9
Cost of sales	609.6	483.4
Gross margin	662.1	442.5
Assets	6,105.6		5,976.9
Nitrogen | Ammonia
Segment data
Net sales	401.7	202.5
Nitrogen | Granular urea
Segment data
Net sales	349.4	224.3
Nitrogen | UAN
Segment data
Net sales	423.7	402.3
Nitrogen | AN
Segment data
Net sales	63.8	61.3
Nitrogen | All Other
Segment data
Net sales	33.1	35.5
Phosphate
Segment data
Net sales	255.9	248.1
Cost of sales	206.2	165.6
Gross margin	49.7	82.5
Assets	694.2		696.4
Phosphate | DAP
Segment data
Net sales	209.3	186.0
Phosphate | MAP
Segment data
Net sales	46.6	62.1
Other.
Segment data
Assets	$ 2,817.1		$ 2,301.2