Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Oct. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in AROs
Obligation at beginning of the period		$ 131.6	$ 119.8	$ 103.7
Accretion expense		9.8	9.4	8.7
Liabilities incurred		13.4	2.4	1.0
Expenditures		(6.2)	(6.0)	(8.7)
Changes in estimates		(3.6)	6.0	15.1
Obligation at end of the period		145.0	131.6	119.8
Change of estimate recorded as an increase (decrease) to property, plant and equipment		(6.5)	(0.6)	9.2
Change of estimate charged to earnings		2.9	6.6	5.9
Deposits into trust	53.0
Expected deposits to be made into the escrow account for the benefit of the FDEP		4.0
Total balance in ARO trust		200.8	145.4
Unrecorded AROs		51.0
Phospho-gypsum Stack Costs
Changes in AROs
Obligation at beginning of the period		54.9	52.1	51.5
Accretion expense		4.1	3.9	3.9
Liabilities incurred		12.5
Expenditures		(1.5)	(2.8)	(5.5)
Changes in estimates		0.1	1.7	2.2
Obligation at end of the period		70.1	54.9	52.1
Mine Reclamation Costs
Changes in AROs
Obligation at beginning of the period		67.6	61.3	46.1
Accretion expense		5.3	5.1	4.5
Liabilities incurred		0.9	2.4	1.0
Expenditures		(3.3)	(2.7)	(3.2)
Changes in estimates		(3.8)	1.5	12.9
Obligation at end of the period		66.7	67.6	61.3
Other AROs
Changes in AROs
Obligation at beginning of the period		9.1	6.4	6.1
Accretion expense		0.4	0.4	0.3
Expenditures		(1.4)	(0.5)
Changes in estimates		0.1	2.8
Obligation at end of the period		$ 8.2	$ 9.1	$ 6.4