Segment Disclosures (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 item	Jun. 30, 2012	Dec. 31, 2012
Segment Disclosures
Number of business segments			2
Segment data
Net sales	$ 1,714.9	$ 1,735.6	$ 3,051.4	$ 3,263.2
Cost of sales	849.7	692.3	1,511.1	1,508.1
Gross margin	865.2	1,043.3	1,540.3	1,755.1
Total other operating costs and expenses	41.0	52.1	99.9	108.2
Equity in earnings of operating affiliates	9.5	13.8	21.1	29.3
Operating earnings	833.7	1,005.0	1,461.5	1,676.2
Assets	10,251.6		10,251.6		10,166.9
Ammonia
Segment data
Net sales	586.8	503.5	787.2	905.2
Granular urea
Segment data
Net sales	271.1	361.8	534.7	711.2
UAN
Segment data
Net sales	556.1	527.7	1,094.0	951.4
AN
Segment data
Net sales	65.2	64.1	120.1	127.9
DAP
Segment data
Net sales	137.4	173.7	334.0	383.0
MAP
Segment data
Net sales	52.3	57.8	94.6	104.4
All Other
Segment data
Net sales	46.0	47.0	86.8	80.1
Nitrogen
Segment data
Net sales	1,525.2	1,504.1	2,622.8	2,775.8
Cost of sales	678.0	511.2	1,128.0	1,120.8
Gross margin	847.2	992.9	1,494.8	1,655.0
Assets	6,276.4		6,276.4		5,991.5
Nitrogen | Ammonia
Segment data
Net sales	586.8	503.5	787.2	905.2
Nitrogen | Granular urea
Segment data
Net sales	271.1	361.8	534.7	711.2
Nitrogen | UAN
Segment data
Net sales	556.1	527.7	1,094.0	951.4
Nitrogen | AN
Segment data
Net sales	65.2	64.1	120.1	127.9
Nitrogen | All Other
Segment data
Net sales	46.0	47.0	86.8	80.1
Phosphate
Segment data
Net sales	189.7	231.5	428.6	487.4
Cost of sales	171.7	181.1	383.1	387.3
Gross margin	18.0	50.4	45.5	100.1
Assets	816.1		816.1		795.2
Phosphate | DAP
Segment data
Net sales	137.4	173.7	334.0	383.0
Phosphate | MAP
Segment data
Net sales	52.3	57.8	94.6	104.4
Other.
Segment data
Assets	$ 3,159.1		$ 3,159.1		$ 3,380.2