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Write-Downs of Long-Lived Assets - Breakdowns of Recognized Impairment Losses for Difference between Carrying Amounts and Fair Values Reflected as Write-Downs of Long-Lived Assets (Parenthetical) (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Mar. 31, 2022
Impaired Long-Lived Assets Held and Used [Line Items]      
Write-downs of long-lived assets ¥ 134 ¥ 243 ¥ 12,749
Property, Plant and Equipment, Other Types      
Impaired Long-Lived Assets Held and Used [Line Items]      
Write-downs of long-lived assets [1] ¥ 134 ¥ 241 11,878
Property, Plant and Equipment, Other Types | Property under Facility Operations      
Impaired Long-Lived Assets Held and Used [Line Items]      
Write-downs of long-lived assets     31,205
Property, Plant and Equipment, Other Types | Coal-biomass co-fired power plants [Member]      
Impaired Long-Lived Assets Held and Used [Line Items]      
Write-downs of long-lived assets     19,564
Property, Plant and Equipment, Other Types | Aircraft      
Impaired Long-Lived Assets Held and Used [Line Items]      
Write-downs of long-lived assets     ¥ 2,331
[1] For the “Others”, the numbers of properties are omitted. Write-downs of long-lived assets for fiscal 2022 include write-downs of ¥31,205 million of property under facility operations and others held by subsidiaries, of which ¥19,564 million related to write-downs of two coal-biomass co-fired power plants, and ¥2,331 million of two aircraft.