Fair Value Measurements (Narrative) (Detail) - Commodity Swaps And Options [Member] - Level 3 [Member]	Dec. 31, 2020 Grade
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average Risk Grade	14.0
Weighted average loss severity in the event of default on commodity swaps	10.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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