Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Millions	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Nov. 30, 2015	Aug. 31, 2015	May. 31, 2015	Feb. 28, 2015	Nov. 30, 2014	Aug. 31, 2014	May. 31, 2014	Feb. 28, 2014	May. 31, 2015	May. 31, 2014	Aug. 31, 2015	Aug. 31, 2014	Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2013
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ 7.7	$ (37.9)	$ 17.3	$ (3.3)	$ 11.9	$ (10.5)	$ (49.2)	$ (2.2)	$ 14.0	$ (51.4)	$ (23.9)	$ (61.9)	$ (16.2)	$ (50.0)	$ 162.9
Other comprehensive (loss) income:
Amortization of net actuarial losses, net of $31.3 million, $20.4 million, and $1.2 million of income taxes in fiscal 2015, 2014, and 2013, respectively		11.8	12.3	12.1	7.4	7.7	7.8	7.7	24.4	15.5	36.2	23.2	49.4	31.1	91.3
Actuarial (losses) gains, net of $36.9 million, $89.8 million, and $1.1 million of income taxes in fiscal 2015, 2014, and 2013, respectively				0.0	(136.0)								(56.6)	(136.0)	167.6
Amortization of prior service credits, net of $0.4 million, $0.4 million and $0.1 million of income taxes in fiscal 2015, 2014, and 2013, respectively													(0.8)	(0.5)	(0.9)
Comprehensive (loss) income		$ (26.1)	$ 29.6	$ 8.8	$ (116.7)	$ (2.8)	$ (41.4)	$ 5.5	$ 38.4	$ (35.9)	$ 12.3	$ (38.7)	$ (24.2)	$ (155.4)	$ 420.9