Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		9 Months Ended
	May. 31, 2015	Aug. 31, 2014	May. 31, 2014	Feb. 28, 2014	May. 31, 2015	May. 31, 2014	Aug. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 18.4	$ (9.9)	$ (50.9)	$ (2.3)	$ 14.5	$ (53.2)	$ (63.1)
Other comprehensive income:
Amortization of actuarial losses and prior service credits, net of income taxes	12.2		7.7		24.4	15.2
Comprehensive income (loss)	$ 30.6		$ (43.2)		$ 38.9	$ (38.0)