Selected Condensed Consolidating Financial Statements of Parent, Issuer, Guarantors and Non-Guarantors - Noncash Operating, Investing and Financing Activities (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Parent [Member]
Operating activities:
Intercompany receivables		$ (140.9)
Investing activities:
Intercompany capital investment		(10,396.2)
Intercompany return of capital		563.0
Financing activities:
Intercompany capital distribution		(563.0)
Issuer [Member]
Investing activities:
Intercompany notes issued		(3,800.0)
Intercompany notes proceeds		4,519.8
Intercompany capital investment		(5,434.8)
Intercompany return of capital		1,478.0
Financing activities:
Intercompany notes borrowing		3,800.0
Intercompany capital receipt		10,396.2
Intercompany capital distribution		(563.0)
Guarantor Subsidiaries [Member]
Investing activities:
Intercompany notes issued	$ (29.1)	(4,519.8)
Intercompany notes proceeds	12.3	4,519.8
Intercompany capital investment	(0.6)	(5,983.6)
Intercompany return of capital		915.0
Financing activities:
Intercompany notes borrowing		457.5
Intercompany notes payments		(457.5)
Intercompany capital receipt		4,977.3
Intercompany capital distribution		(457.5)
Non-Guarantor Subsidiaries [Member]
Operating activities:
Intercompany payables		140.9
Investing activities:
Intercompany notes issued		(8,057.5)
Intercompany notes proceeds		4,257.5
Financing activities:
Intercompany notes borrowing	29.1	12,119.8
Intercompany notes payments	(12.3)	(12,839.6)
Intercompany capital receipt	0.6	6,441.1
Intercompany capital distribution		(1,372.5)
Intercompany dividends paid	(31.2)	(572.4)
Eliminations [Member]
Operating activities:
Intercompany receivables		140.9
Intercompany payables		(140.9)
Investing activities:
Intercompany notes issued	29.1	16,377.3
Intercompany notes proceeds	(12.3)	(13,297.1)
Intercompany capital investment	0.6	21,814.6
Intercompany return of capital		(2,956.0)
Financing activities:
Intercompany notes borrowing	(29.1)	(16,377.3)
Intercompany notes payments	12.3	13,297.1
Intercompany capital receipt	(0.6)	(21,814.6)
Intercompany capital distribution		2,956.0
Intercompany dividends paid	$ 31.2	$ 572.4