Equity Method Investments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Equity method investments
Investments in and advances to affiliates	$ 991.9		$ 991.9		$ 928.6
Condensed income statement information:
Equity in earnings of operating affiliates	10.2	15.0	39.5	40.7
Equity in earnings of non-operating affiliates-net of taxes	23.9	16.7	48.8	35.0
Operating Equity Method Investments
Equity method investments
Investments in and advances to affiliates	408.1		408.1		413.1
Condensed income statement information:
Net sales	67.8	116.4	249.0	272.7
Net earnings	20.5	39.8	83.0	93.5
Equity in earnings of operating affiliates	10.2	15.0	39.5	40.7
Condensed balance sheet information:
Current assets	117.0		117.0		126.6
Long-term assets	160.1		160.1		147.2
Total assets	277.1		277.1		273.8
Current liabilities	42.6		42.6		41.1
Long-term liabilities	23.5		23.5		24.2
Equity	211.0		211.0		208.5
Total liabilities and equity	277.1		277.1		273.8
Equity Method Investments
Carrying value of investments	408.1		408.1
Carrying value of investments in excess of the entity's share of the affiliates' book value	302.6		302.6
Operating Equity Method Investments | Property, plant and equipment | Maximum
Equity Method Investments
Number of years that the increased basis for property, plant and equipment and identifiable intangibles will be depreciated			22 years
Operating Equity Method Investments | Gas contract | Maximum
Equity Method Investments
Number of years that the increased basis for property, plant and equipment and identifiable intangibles will be depreciated			12 years
Operating Equity Method Investments | Point Lisas Nitrogen Limited (PLNL)
Equity method investments
Ownership interest (as a percent)	50.00%		50.00%
Equity Method Investments
Obligation to purchase ammonia (as a percent)			50% of the ammonia produced by PLNL
Purchases of ammonia from PLNL since date acquisition	31.4	51.6	113.5	122.2
Operating Equity Method Investments | Ammonia storage joint venture
Equity method investments
Ownership interest (as a percent)	50.00%		50.00%
Non-Operating Equity Method Investments
Equity method investments
Investments in and advances to affiliates	583.8		583.8		515.5
Condensed income statement information:
Net sales	685.6	896.8	2,182.6	2,178.2
Net earnings	54.2	39.7	116.9	89.7
Equity in earnings of non-operating affiliates-net of taxes	23.9	16.7	48.8	35.0
Condensed balance sheet information:
Current assets	759.1		759.1		504.2
Long-term assets	290.1		290.1		293.4
Total assets	1,049.2		1,049.2		797.6
Current liabilities	472.2		472.2		339.5
Long-term liabilities	139.9		139.9		149.4
Equity	437.1		437.1		308.7
Total liabilities and equity	1,049.2		1,049.2		797.6
Equity Method Investments
Amount of consolidated retained earnings	55.3		55.3
Non-Operating Equity Method Investments | KEYTRADE AG
Equity method investments
Ownership interest (as a percent)	50.00%		50.00%
Equity Method Investments
Carrying value of investments	571.4		571.4
Carrying value of investments in excess of the entity's share of the affiliates' book value	352.7		352.7
Percentage rate of debt financing of subordinated notes to Keytrade			LIBOR
Percentage on debt instrument in addition to LIBOR Rate	1.00%		1.00%
Amount of outstanding advances	12.4		12.4		12.4
Non-Operating Equity Method Investments | KEYTRADE AG | Maximum
Equity Method Investments
Number of years that the increased basis for property, plant and equipment and identifiable intangibles will be depreciated			14 years
Non-Operating Equity Method Investments | KEYTRADE AG | Minimum
Equity Method Investments
Number of years that the increased basis for property, plant and equipment and identifiable intangibles will be depreciated			2 years
Non-Operating Equity Method Investments | GrowHow
Equity method investments
Ownership interest (as a percent)	50.00%		50.00%
Equity Method Investments
Percentage rate of debt financing of subordinated notes to Keytrade			LIBOR
Percentage on debt instrument in addition to LIBOR Rate	0.20%		0.20%
Amount of outstanding advances	$ 40.5		$ 40.5