Earnings Per Share - Summary of Basic and Diluted EPS (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ (37.5)	$ (24.4)	$ (8.7)	$ (71.6)
Income (Loss) from Continuing Operations, Per Basic Share	$ (0.18)	$ (0.12)	$ (0.04)	$ (0.36)
Income (Loss) from Continuing Operations, Per Diluted Share	(0.18)	(0.12)	(0.04)	(0.36)
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	0.00	(0.29)	2.38	1.01
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	$ 0.00	$ (0.29)	$ 2.38	$ 1.01
Net Income (Loss) Attributable to Parent	$ (37.1)	$ (82.1)	$ 470.3	$ 130.1
Net (loss) income attributable to controlling interest	$ (37.1)	$ (82.1)	$ 470.3	$ 130.1
Dilutive adjustments to income (loss) attributable to common shares from assumed conversion of preferred shares, net of tax:
Weighted-average common shares outstanding - basic and diluted	201,646	199,981	201,105	199,579
Net (loss) income per common share attributable to controlling interest:
Earnings Per Share, Basic	$ (0.18)	$ (0.41)	$ 2.34	$ 0.65
Earnings Per Share, Diluted	$ (0.18)	$ (0.41)	$ 2.34	$ 0.65
Discontinued Operations, Held-for-sale [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ 0.4	$ (57.7)
Net Income (Loss) Attributable to Parent			$ 454.5	$ 160.2
HGI | Discontinued Operations, Held-for-sale [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income (Loss) Attributable to Parent			$ 479.0	$ 201.7
Restricted stock awards
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6	393	44	846
Stock option awards
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	976	1,820	1,275	1,708
Warrant [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	125	235	113	177