Equity Method Investments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			6 Months Ended	12 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Operating Equity Method Investments	Jun. 30, 2013 Operating Equity Method Investments	Jun. 30, 2014 Operating Equity Method Investments	Jun. 30, 2013 Operating Equity Method Investments	Dec. 31, 2013 Operating Equity Method Investments	Jun. 30, 2014 Operating Equity Method Investments Property, plant and equipment Maximum	Jun. 30, 2014 Operating Equity Method Investments Gas contract Maximum	Jun. 30, 2014 Operating Equity Method Investments Point Lisas Nitrogen Limited (PLNL)	Jun. 30, 2013 Operating Equity Method Investments Point Lisas Nitrogen Limited (PLNL)	Jun. 30, 2014 Operating Equity Method Investments Point Lisas Nitrogen Limited (PLNL)	Jun. 30, 2013 Operating Equity Method Investments Point Lisas Nitrogen Limited (PLNL)	Jun. 30, 2014 Operating Equity Method Investments Ammonia storage joint venture	Jun. 30, 2014 Non-Operating Equity Method Investments	Jun. 30, 2013 Non-Operating Equity Method Investments	Jun. 30, 2014 Non-Operating Equity Method Investments	Jun. 30, 2013 Non-Operating Equity Method Investments	Dec. 31, 2013 Non-Operating Equity Method Investments	Jun. 30, 2014 Non-Operating Equity Method Investments KEYTRADE AG	Dec. 31, 2013 Non-Operating Equity Method Investments KEYTRADE AG	Jun. 30, 2014 Non-Operating Equity Method Investments KEYTRADE AG Maximum	Jun. 30, 2014 Non-Operating Equity Method Investments GrowHow
Equity method investments
Investments in and advances to affiliates	$ 943.0		$ 943.0		$ 926.0	$ 371.3		$ 371.3		$ 379.7								$ 571.7		$ 571.7		$ 546.3
Ownership interest (as a percent)													50.00%		50.00%		50.00%						50.00%			50.00%
Condensed statement of operations information:
Net sales						62.3	75.2	137.5	171.6									437.3	712.5	1,007.6	1,306.6
Net earnings						9.7	23.7	34.5	55.9									10.0	3.3	32.4	10.3
Equity in earnings of operating affiliates	2.1	9.5	17.9	21.1		2.1	9.5	17.9	21.1									1.7	(1.7)	5.2	(1.0)
Equity in earnings of non-operating affiliates - net of taxes	1.7	(1.7)	5.2	(1.0)
Condensed balance sheet information:
Current assets						87.9		87.9		84.3								542.2		542.2		540.3
Noncurrent assets						138.8		138.8		147.3								331.1		331.1		319.3
Total assets						226.7		226.7		231.6								873.3		873.3		859.6
Current liabilities						41.1		41.1		36.5								286.1		286.1		310.6
Noncurrent liabilities						25.0		25.0		25.0								164.5		164.5		168.9
Equity						160.6		160.6		170.1								422.7		422.7		380.1
Total liabilities and equity						226.7		226.7		231.6								873.3		873.3		859.6
Equity Method Investments
Carrying value of investments						371.3		371.3										559.3		559.3
Carrying value of investments in excess of the entity's share of the affiliates' book value						291.0		291.0										348.0		348.0
Number of years that the increased basis for property, plant and equipment and identifiable intangibles will be amortized											19 years	9 years													11 years
Obligation to purchase ammonia (as a percent)															50% of the ammonia produced by PLNL
Purchases of ammonia from PLNL													32.0	41.8	66.0	80.2
Percentage rate of debt financing of subordinated notes to Keytrade																							LIBOR	LIBOR
Percentage on debt instrument in addition to LIBOR Rate																							1.00%	1.00%
Amount of outstanding advances																							12.4	12.4
Recognized interest income on advances																				0.1	0.1
Undistributed earnings from equity method investees																		$ 29.8		$ 29.8