Debt - Schedule of Long-term Debt Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Long Term Debt	$ 4,560,000
Finance lease obligation	8,631	$ 0
Total long-term debt	4,568,631	3,560,000
Less:
Net original issue (premium) / discount on unsecured senior notes and debentures	583	193
Debt issuance cost	36,104	30,355
Current maturities	165	0
Long-term debt	4,531,779	3,529,452
Unsecured 3.00% Senior Notes, due 2027
Debt Instrument [Line Items]
Long Term Debt	$ 500,000	500,000
Less:
Interest rate	3.00%
Unsecured 2.625% Senior Notes, due 2029
Debt Instrument [Line Items]
Long Term Debt	$ 300,000	0
Less:
Interest rate	2.625%
Unsecured 5.95% Senior Notes, due 2034
Debt Instrument [Line Items]
Long Term Debt	$ 200,000	200,000
Less:
Interest rate	5.95%
Unsecured 5.50% Senior Notes, due 2041
Debt Instrument [Line Items]
Long Term Debt	$ 400,000	400,000
Less:
Interest rate	5.50%
Unsecured 4.15% Senior Notes, due 2043
Debt Instrument [Line Items]
Long Term Debt	$ 500,000	500,000
Less:
Interest rate	4.15%
Unsecured 4.125% Senior Notes, due 2044
Debt Instrument [Line Items]
Long Term Debt	$ 750,000	750,000
Less:
Interest rate	4.125%
Unsecured 4.30% Senior Notes, due 2048
Debt Instrument [Line Items]
Long Term Debt	$ 600,000	600,000
Less:
Interest rate	4.30%
Unsecured 4.125% Senior Notes, due 2049
Debt Instrument [Line Items]
Long Term Debt	$ 450,000	450,000
Less:
Interest rate	4.125%
Unsecured 3.375% Senior Notes, due 2049
Debt Instrument [Line Items]
Long Term Debt	$ 500,000	0
Less:
Interest rate	3.375%
Floating-rate term loan, due 2022
Debt Instrument [Line Items]
Long Term Debt	$ 200,000	0
Medium term Series A notes, 1995-1, 6.67%, due 2025
Debt Instrument [Line Items]
Long Term Debt	$ 10,000	10,000
Less:
Interest rate	6.67%
Unsecured 6.75% Debentures, due 2028
Debt Instrument [Line Items]
Long Term Debt	$ 150,000	$ 150,000
Less:
Interest rate	6.75%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt discount (premium).

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

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Amount of long-term debt and lease obligation, classified as noncurrent.

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Amount of long-term debt and lease obligation, classified as current.

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Amount of long-term debt and lease obligation, including portion classified as current.

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