Segment Disclosures (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 item	Sep. 30, 2012	Dec. 31, 2012
Segment Disclosures
Number of business segments			2
Segment data
Net sales	$ 1,097.0	$ 1,359.4	$ 4,148.4	$ 4,622.6
Cost of sales	710.9	657.4	2,222.0	2,165.5
Gross margin	386.1	702.0	1,926.4	2,457.1
Total other operating costs and expenses	11.9	45.1	111.8	153.3
Equity in earnings of operating affiliates	11.2	10.2	32.3	39.5
Operating earnings	385.4	667.1	1,846.9	2,343.3
Assets	10,799.0		10,799.0		10,166.9
Nitrogen
Segment data
Assets	6,471.5		6,471.5		5,991.5
Phosphate
Segment data
Assets	779.2		779.2		795.2
Other
Segment data
Assets	3,548.3		3,548.3		3,380.2
Operating segments
Segment data
Net sales	1,097.0	1,359.4	4,148.4	4,622.6
Cost of sales	710.9	657.4	2,222.0	2,165.5
Gross margin	386.1	702.0	1,926.4	2,457.1
Operating segments | Ammonia
Segment data
Net sales	211.3	259.1	998.5	1,164.3
Operating segments | Granular urea
Segment data
Net sales	185.3	262.7	720.0	973.9
Operating segments | UAN
Segment data
Net sales	393.6	474.4	1,487.6	1,425.8
Operating segments | AN
Segment data
Net sales	46.4	53.7	166.5	181.6
Operating segments | DAP
Segment data
Net sales	154.3	200.2	488.3	583.2
Operating segments | MAP
Segment data
Net sales	66.4	64.0	161.0	168.4
Operating segments | All Other
Segment data
Net sales	39.7	45.3	126.5	125.4
Operating segments | Nitrogen
Segment data
Net sales	876.3	1,095.2	3,499.1	3,871.0
Cost of sales	517.9	456.6	1,645.9	1,577.4
Gross margin	358.4	638.6	1,853.2	2,293.6
Operating segments | Nitrogen | Ammonia
Segment data
Net sales	211.3	259.1	998.5	1,164.3
Operating segments | Nitrogen | Granular urea
Segment data
Net sales	185.3	262.7	720.0	973.9
Operating segments | Nitrogen | UAN
Segment data
Net sales	393.6	474.4	1,487.6	1,425.8
Operating segments | Nitrogen | AN
Segment data
Net sales	46.4	53.7	166.5	181.6
Operating segments | Nitrogen | All Other
Segment data
Net sales	39.7	45.3	126.5	125.4
Operating segments | Phosphate
Segment data
Net sales	220.7	264.2	649.3	751.6
Cost of sales	193.0	200.8	576.1	588.1
Gross margin	27.7	63.4	73.2	163.5
Operating segments | Phosphate | DAP
Segment data
Net sales	154.3	200.2	488.3	583.2
Operating segments | Phosphate | MAP
Segment data
Net sales	$ 66.4	$ 64.0	$ 161.0	$ 168.4