Earnings Per Share - Summary of Basic and Diluted EPS (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income (loss) attributable to common and participating preferred stockholders	$ (109.8)	$ (39.0)
Participating shares at end of period:
Common shares outstanding	196,879	139,574
Preferred shares (as-converted basis)	0	61,986
Total	196,879	201,560
Percentage of income (loss) allocated to:
Common shares	100.00%	100.00%
Preferred shares (a)	0.00%	0.00%
Net income (loss) attributable to common shares - basic	$ (109.8)	$ (39.0)
Weighted-average common shares outstanding - basic	196,997	139,173
Net loss per common share attributable to controlling interest:
Basic (in dollars per share)	$ (0.56)	$ (0.28)
Diluted (in dollars per share)	$ (0.56)	$ (0.28)