v3.26.1
Employee Benefits - Summary of Defined Benefit Plans (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Japanese plans [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year ¥ 220,652  
Remeasurement    
Balance at end of year 243,769 ¥ 220,652
Japanese plans [Member] | Present value of defined benefit obligations [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 1,729,554 1,898,339
Current service cost 62,259 76,758
Interest cost / income 37,798 26,290
Remeasurement    
Changes in demographic assumptions (2,153) (3,635)
Changes in financial assumptions (181,466) (181,128)
Other 4,347 (385)
Past service cost (409) (184)
Plan participants' contributions 1,027 1,065
Benefits paid (86,522) (86,871)
Effect of changes in exchange rates and other (86,937) (696)
Balance at end of year 1,477,496 1,729,554
Japanese plans [Member] | Fair value of plan assets [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 2,081,009 2,128,476
Interest cost / income 48,763 29,462
Remeasurement    
Actual return on plan assets, excluding interest income 106,715 (66,135)
Employer contributions 48,385 35,669
Plan participants' contributions 1,027 1,065
Benefits paid (46,738) (47,528)
Effect of changes in exchange rates and other (286,583) 0
Balance at end of year 1,952,578 2,081,009
Japanese plans [Member] | The impact of minimum funding requirement and asset ceiling [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 572,107  
Remeasurement    
Balance at end of year 718,851 572,107
Foreign plans [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 350,817  
Remeasurement    
Balance at end of year 391,088 350,817
Foreign plans [Member] | Present value of defined benefit obligations [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 1,622,053 1,651,016
Current service cost 50,747 49,225
Interest cost / income 81,582 81,411
Remeasurement    
Changes in demographic assumptions 1,944 68
Changes in financial assumptions (33,796) (48,712)
Other 44,858 (15,579)
Past service cost (591) (3,027)
Plan participants' contributions 4,657 4,355
Benefits paid (84,889) (76,204)
Effect of changes in exchange rates and other 114,563 (20,499)
Balance at end of year 1,801,130 1,622,053
Foreign plans [Member] | Fair value of plan assets [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 1,271,236 1,284,918
Interest cost / income 63,712 57,149
Remeasurement    
Actual return on plan assets, excluding interest income 892 (33,874)
Employer contributions 19,099 19,016
Plan participants' contributions 4,657 4,355
Benefits paid (47,090) (42,023)
Effect of changes in exchange rates and other 97,536 (18,305)
Balance at end of year ¥ 1,410,042 ¥ 1,271,236