Segment Disclosures (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 item	Sep. 30, 2011	Dec. 31, 2011
Segment Disclosures
Number of business segments			2
Segment data
Net sales	$ 1,359.4	$ 1,403.8	$ 4,622.6	$ 4,379.5
Cost of sales	657.4	765.8	2,165.5	2,349.1
Gross margin	702.0	638.0	2,457.1	2,030.4
Total other operating costs and expenses	45.1	70.7	153.3	109.7
Equity in earnings of operating affiliates	10.2	15.0	39.5	40.7
Operating earnings	667.1	582.3	2,343.3	1,961.4
Assets	10,182.7		10,182.7		8,974.5
Ammonia
Segment data
Net sales	259.1	222.9	1,164.3	1,009.7
Granular urea
Segment data
Net sales	262.7	298.0	973.9	805.3
UAN
Segment data
Net sales	474.4	495.7	1,425.8	1,430.2
AN
Segment data
Net sales	53.7	65.4	181.6	196.3
DAP
Segment data
Net sales	200.2	219.7	583.2	617.5
MAP
Segment data
Net sales	64.0	66.1	168.4	213.0
All Other
Segment data
Net sales	45.3	36.0	125.4	107.5
Nitrogen
Segment data
Net sales	1,095.2	1,118.0	3,871.0	3,549.0
Cost of sales	456.6	565.9	1,577.4	1,771.8
Gross margin	638.6	552.1	2,293.6	1,777.2
Assets	6,015.5		6,015.5		5,976.9
Nitrogen | Ammonia
Segment data
Net sales	259.1	222.9	1,164.3	1,009.7
Nitrogen | Granular urea
Segment data
Net sales	262.7	298.0	973.9	805.3
Nitrogen | UAN
Segment data
Net sales	474.4	495.7	1,425.8	1,430.2
Nitrogen | AN
Segment data
Net sales	53.7	65.4	181.6	196.3
Nitrogen | All Other
Segment data
Net sales	45.3	36.0	125.4	107.5
Phosphate
Segment data
Net sales	264.2	285.8	751.6	830.5
Cost of sales	200.8	199.9	588.1	577.3
Gross margin	63.4	85.9	163.5	253.2
Assets	693.1		693.1		696.4
Phosphate | DAP
Segment data
Net sales	200.2	219.7	583.2	617.5
Phosphate | MAP
Segment data
Net sales	64.0	66.1	168.4	213.0
Other.
Segment data
Assets	$ 3,474.1		$ 3,474.1		$ 2,301.2