Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net (loss) earnings including noncontrolling interest	$ (104.2)	$ 301.2	$ 1,001.8
Other comprehensive income (loss), net of tax
Foreign currency translation gain (loss), net of tax (expense) benefit	240.5	192.3	(1,027.1)
Net actuarial gain (loss) and prior service cost, net of tax (expense) benefit	6.3	(3.2)	1.0
Realized gain on interest rate swap, net of tax (expense) benefit	1.7	1.5	2.0
Net gain (loss) on marketable securities held in trust fund, net of tax (expense) benefit	1.7	(7.8)	0.0
Other comprehensive income (loss)	250.2	182.8	(1,024.1)
Comprehensive income (loss)	146.0	484.0	(22.3)
Less: Comprehensive income (loss) attributable to noncontrolling interest	2.6	5.5	(3.5)
Comprehensive income (loss) attributable to Mosaic	$ 143.4	$ 478.5	$ (18.8)