Derivative Financial Instruments and Hedging Activities - Gross Fair Values of Derivative Assets, Derivative Liabilities, and Margin Deposits (Cash Collateral) (Details) - USD ($) $ in Thousands	Feb. 28, 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	$ 1,003,227	$ 358,300
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	978,487	345,935
Derivative Liability, Fair Value, Gross Liability	579,671	412,809
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	551,923	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	980,141	327,493
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	961,292	324,513
Derivative Liability, Fair Value, Gross Liability	515,002	343,343
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	493,145	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	7,221	11,809
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	1,330	2,424
Derivative Liability, Fair Value, Gross Liability	64,669	69,466
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	58,778	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	15,865	18,998
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 15,865	$ 18,998