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Income Taxes (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Income Taxes (Detail) - USD ($) $ in Millions	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Income Taxes
Effective tax rate of income (loss) before income taxes	23.20%	21.70%	21.20%	20.50%
Renewable Natural Gas [Member]
Income Taxes
Tax credits and adjustments	$ 29	$ 43	$ 53	$ 89
Tax credits from production and sales activity	9		44
Renewable Natural Gas [Member] \| First quarter of 2026 [Member]
Income Taxes
Tax credits from production and sales activity			17
Renewable Natural Gas [Member] \| 2025 operations [Member]
Income Taxes
Tax credits from production and sales activity			27
Low income housing investments [Member]
Income Taxes
Investment proportional amortization tax impact	26	25	48	45
Income tax benefit from low-income housing investments	$ 35	35	65	62
Variable interest entities interest expense		$ 8	$ 15	$ 17