Schedule II - Condensed Financial Information of Registrant - Condensed Statements of Cash Flows of Registrant (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ (36.6)	$ (51.4)	$ 542.3	$ 209.4
Adjustments to reconcile net income (loss) to operating cash flows from continuing operations:
Depreciation of properties and amortization of intangibles			67.2	61.7
Stock-based compensation	3.1	14.0	1.1	23.5
Amortization of debt issuance costs			13.5	8.2
Amortization of debt discount			(2.3)	0.9
Non-cash restructuring				1.9
Dividends from subsidiaries			3.1	6.1
Changes in operating assets and liabilities:
Net change in cash due to continuing operating activities			(185.8)	109.2
Cash flows from investing activities:
Proceeds from investments sold, matured or repaid			0.9
Capital expenditures			(34.2)	(37.1)
Net change in cash due to continuing investing activities			1,297.9	(804.1)
Cash flows from financing activities:
Payments of Debt Issuance Costs			(0.3)	(3.8)
Share based award tax withholding payments			(22.7)	(37.4)
Other financing activities, net			10.0	5.5
Net change in cash due to continuing financing activities			(588.9)	545.5
Cash and Cash Equivalents, Period Increase (Decrease)			488.7	(170.6)
Cash and cash equivalents at beginning of period			270.1	465.2
Cash and cash equivalents at end of period	$ 758.8	$ 294.6	$ 758.8	$ 294.6