Financing Agreements (Schedule of Total Debt) (Details)	6 Months Ended
	Mar. 31, 2019 USD ($) derivative	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	May 31, 2018 USD ($)	Feb. 28, 2017 USD ($)
Debt Instrument [Line Items]
Repayments of Long-term Debt	$ 100,000	$ 54,900,000
Long-term Debt, by Current and Noncurrent [Abstract]
Current portion of long-term debt	33,200,000		$ 100,000
Total Short-term borrowings	1,989,100,000		1,972,900,000
Revolving credit facility, matures September 2021	224,700,000		182,500,000
Total Long-term debt	1,764,400,000		1,790,400,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	8,000,000.0
Long-term Debt, by Current and Noncurrent [Abstract]
Revolving credit facility, matures September 2021	5,000,000.0		0
Line of Credit Facility, Maximum Borrowing Capacity	700,000,000.0
Line of Credit Facility, Remaining Borrowing Capacity	$ 687,000,000.0
Senior Secured Credit Facilities [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate During Period	4.00%
Senior Secured Term Loan A [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Year Three	$ 0
Line of Credit Facility, Interest Rate During Period	0.00%
Long-term Debt, by Current and Noncurrent [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,462,500,000
Total Long-term debt	998,100,000		1,029,700,000
Long-term Debt, Maturities, Repayments of Principal in Year Five	$ 0
Senior Unsecured 5.75% Notes due on September 1, 2023 [Member]
Long-term Debt, by Current and Noncurrent [Abstract]
Unsecured debenture interest rate	5.75%
Debt Instrument, Face Amount	$ 425,000,000.0
Total Long-term debt	$ 421,200,000		420,800,000
Senior Unsecured 5.00% Notes due on February 14, 2025 [Member]
Long-term Debt, by Current and Noncurrent [Abstract]
Unsecured debenture interest rate	5.00%
Debt Instrument, Face Amount					$ 300,000,000.0
Total Long-term debt	$ 296,700,000		296,400,000
Unsecured 7.00% Debentures Due on February 15, 2024 [Member]
Long-term Debt, by Current and Noncurrent [Abstract]
Unsecured debenture interest rate	7.00%
Total Short-term borrowings	$ 13,500,000		13,600,000
Unsecured 6.75% Debentures Due on December 15, 2027 [Member]
Long-term Debt, by Current and Noncurrent [Abstract]
Unsecured debenture interest rate	6.75%
Total Short-term borrowings	$ 29,600,000		29,500,000
Securitization Program [Member]
Long-term Debt, by Current and Noncurrent [Abstract]
Unsecured debenture interest rate	0.675%
Debt Instrument, Face Amount				$ 110,000,000.0
Principal Amount Outstanding on Loans Securitized or Asset-backed Financing Arrangement	$ 110,000,000.0		110,000,000.0
Note Securitization Facility [Member]
Long-term Debt, by Current and Noncurrent [Abstract]
Debt Instrument, Face Amount				$ 90,000,000.0
Principal Amount Outstanding on Loans Securitized or Asset-backed Financing Arrangement	81,500,000		72,400,000
Other Financing Agreements [Member]
Long-term Debt, by Current and Noncurrent [Abstract]
Total Short-term borrowings	$ 300,000		$ 400,000
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, Number of Instruments Held | derivative	5