Regulatory - Additional Information (Detail) - USD ($) $ in Millions				12 Months Ended
	Jan. 31, 2027	Jan. 31, 2026	Jan. 31, 2025	May 31, 2025	Jun. 30, 2024	Dec. 31, 2023
Public Utilities General Disclosures [Line Items]
Accumulated depreciation					$ 3,548	$ 3,443
Scenario Forecast [Member]
Public Utilities General Disclosures [Line Items]
Effect of base rate adjustment on revenue	$ 72	$ 100	$ 297
Adjustments to fuel and capacity charges reduction over period				$ 138