Fair Value Measurements (Assets and Liabilities Accounted for at Fair Value on Recurring Basis) (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash collateral netted with derivative liabilities	$ 13	$ 29
Fair Value, Recurring \| Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - netting and collateral	(282)	(220)
Derivative asset, net carrying value on balance sheet	21	24
Commodity derivative instruments, assets - collateral pledged not offset	36	73
Commodity derivative instruments, liabilities - netting and collateral	(295)	(249)
Derivative liability, net carrying value on balance sheet	0	0
Commodity derivative instruments, liabilities - collateral pledged not offset	0	0
Fair Value, Recurring \| Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - netting and collateral	0	0
Derivative liability, net carrying value on balance sheet	69	61
Commodity derivative instruments, liabilities - collateral pledged not offset	0	0
Fair Value, Recurring \| Level 1 \| Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross	302	244
Commodity derivative instruments, liabilities - gross	295	249
Fair Value, Recurring \| Level 1 \| Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - gross	0	0
Fair Value, Recurring \| Level 2 \| Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross	1	0
Commodity derivative instruments, liabilities - gross	0	0
Fair Value, Recurring \| Level 2 \| Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - gross	0	0
Fair Value, Recurring \| Level 3 \| Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross	0	0
Commodity derivative instruments, liabilities - gross	0	0
Fair Value, Recurring \| Level 3 \| Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - gross	$ 69	$ 61

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