Derivative Financial Instruments and Hedging Activities - Gross Fair Values of Derivative Assets, Derivative Liabilities, and Margin Deposits (Cash Collateral) (Details) - USD ($) $ in Thousands	May 31, 2021	Aug. 31, 2020
Reconciliation of gross and net fair value of assets and liabilities subject to offsetting arrangements [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 889,233	$ 358,300
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	873,621	345,935
Derivative Liability, Fair Value, Gross Liability	595,565	412,809
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	577,144	396,890
Not Designated as Hedging Instrument | Commodity derivatives
Reconciliation of gross and net fair value of assets and liabilities subject to offsetting arrangements [Line Items]
Derivative Asset, Fair Value, Gross Asset	843,728	327,493
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	835,502	324,513
Derivative Liability, Fair Value, Gross Liability	585,658	343,343
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	574,623	336,809
Not Designated as Hedging Instrument | Foreign exchange derivatives
Reconciliation of gross and net fair value of assets and liabilities subject to offsetting arrangements [Line Items]
Derivative Asset, Fair Value, Gross Asset	29,332	11,809
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	21,946	2,424
Derivative Liability, Fair Value, Gross Liability	9,907	69,466
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	2,521	60,081
Not Designated as Hedging Instrument | Embedded Derivative Financial Instruments [Member]
Reconciliation of gross and net fair value of assets and liabilities subject to offsetting arrangements [Line Items]
Derivative Asset, Fair Value, Gross Asset	16,173	18,998
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 16,173	$ 18,998