Earnings Per Share - Summary of Basic and Diluted EPS (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Preferred Stock Dividends, Income Statement Impact		$ (28.0)		$ (33.1)
Preferred Stock, Accretion of Redemption Discount		(12.0)		(36.3)
Preferred Stock Conversions, Inducements		52.6		81.9
Dilutive Adjustments To Income Loss Attributable To Common Stock From Assumed Conversion Of Preferred Stock Net Of Tax		(12.6)		(12.5)
Net income (loss) attributable to common and participating preferred stockholders	49.0	91.6	(77.6)	108.1
Participating shares at end of period:
Common shares outstanding	201,043	140,576	201,043	140,576
Preferred shares (as-converted basis)	0	61,987	0	61,987
Total	201,043	202,563	201,043	202,563
Percentage of income (loss) allocated to:
Common shares	100.00%	69.40%	100.00%	69.40%
Preferred shares (a)	0.00%	30.60%	0.00%	30.60%
Net income (loss) attributable to common shares - basic	49.0	63.6	(77.6)	75.0
Dilutive adjustments to income (loss) attributable to common shares from assumed conversion of preferred shares, net of tax:
Net income (loss) attributable to common shares - diluted	$ 49.0	$ 51.0	$ (77.6)	$ 62.5
Weighted-average common shares outstanding - basic	172,967	140,292	150,675	139,832
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Preferred Stock		62,413		62,555
Dilutive effect of unvested restricted stock and restricted stock units	3,798	1,853		2,231
Dilutive effect of stock options	1,281	662		612
Weighted-average shares outstanding - diluted	178,046	205,220	150,675	205,230
Net income (loss) per common share attributable to controlling interest:
Basic (in dollars per share)	$ 0.28	$ 0.45	$ (0.52)	$ 0.54
Diluted (in dollars per share)	$ 0.28	$ 0.25	$ (0.52)	$ 0.30