Schedule II - Condensed Financial Information of Registrant - Condensed Statements of Operations of Registrant (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Condensed Income Statements, Captions [Line Items]
Stockholders' Equity Attributable to Parent	$ 691.6		$ 691.6		$ 758.0
Consolidated segment revenues	766.1	$ 757.4	1,412.6	$ 1,359.7
Operating expenses:
Operating income	28.9	95.3	55.5	136.6
Other income (expense):
Interest Expense	(67.6)	(77.7)	(143.1)	(156.4)
Other income (expense), net	0.2	(1.4)	1.2	(0.4)
(Loss) income from continuing operations before income taxes	(38.5)	16.2	(86.4)	(20.2)
Income tax (benefit) expense	(1.2)	24.0	(127.2)	29.6
Net (loss) income from continuing operations	(36.6)	(51.4)	542.3	209.4
Net (loss) income attributable to common and participating preferred stockholders	(37.1)	(82.1)	470.3	130.1
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	0.7	(43.6)	501.5	259.2
Net Income (Loss) Attributable to Parent	$ (37.1)	$ (82.1)	470.3	130.1
Discontinued Operations, Held-for-sale [Member]
Condensed Income Statements, Captions [Line Items]
Stockholders' Equity Attributable to Parent					$ 1,536.3
Consolidated segment revenues				0.0
Operating expenses:
Operating income			0.0	0.0
Other income (expense):
Net (loss) income from continuing operations			459.9	187.7
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest			459.9	187.7
Net Income (Loss) Attributable to Parent			454.5	160.2
Discontinued Operations, Held-for-sale [Member] | HGI
Other income (expense):
Net Income (Loss) Attributable to Parent			$ 479.0	$ 201.7