Financial Instruments (Narrative) (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2022 USD ($) counterparty MMcf bbl		Sep. 30, 2021 USD ($)	[1]	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Foreign Currency Forward Contract Hedge Duration	9 years
Net hedging gains (losses) in accumulated other comprehensive loss	$ (802,100)
After tax net hedging gains (losses) in accumulated other comprehensive loss	(584,800)
Pre-Tax Net Hedging Gains (Losses) Reclassified Within Twelve Months	(550,400)
After Tax Net Hedging Gains (Losses) Reclassified Within Twelve Months	(401,300)
Fair market value of derivative liability with a credit-risk related contingency	619,300
Hedging Collateral Deposits	102,370	[1]	$ 88,610		$ 0	$ 0
Less Than $100,000
Derivative Instruments, Gain (Loss) [Line Items]
Fair market value of derivative asset with a credit-risk related contingency	$ 100
Cash Flow Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedge Duration	5 years
Over the Counter Swaps, No Cost Collars and Foreign Currency Forward Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Number of counterparties in which the company holds over-the-counter swap positions | counterparty	18
Number of counterparties in net gain position | counterparty	1
Collateral Received by the Company	$ 0
Hedging Collateral Deposits	102,400
Over the Counter Swaps, No Cost Collars and Foreign Currency Forward Contracts [Member] | Less Than $100,000
Derivative Instruments, Gain (Loss) [Line Items]
Credit risk exposure per counterparty	$ 100
Natural Gas MMCf [Member] | Cash Flow Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Nonmonetary notional amount of price risk cash flow hedge derivatives, natural gas | MMcf	468,400
Crude Oil Bbls [Member] | Cash Flow Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Nonmonetary notional amount of price risk cash flow hedge derivatives, crude oil | bbl	1,368,000
Foreign Currency Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount	$ 57,500
Credit Risk Related Contingency Feature [Member] | Over the Counter Swaps, No Cost Collars and Foreign Currency Forward Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Number of counterparties with a common credit-risk related contingency | counterparty	16

[1] Netting Adjustments represent the impact of legally-enforceable master netting arrangements that allow the Company to net gain and loss positions held with the same counterparties. The net asset or net liability for each counterparty is recorded as an asset or liability on the Company’s balance sheet.