v3.25.2
Employee Benefits - Summary of Defined Benefit Plans (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Japanese plans [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year ¥ 38,092  
Remeasurement    
Balance at end of year 220,652 ¥ 38,092
Japanese plans [Member] | Present value of defined benefit obligations [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 1,898,339 1,964,655
Current service cost 76,758 80,133
Interest cost / income 26,290 21,666
Remeasurement    
Changes in demographic assumptions (3,635) 850
Changes in financial assumptions (181,128) (74,816)
Other (385) (2,926)
Past service cost (184) 418
Plan participants' contributions 1,065 1,143
Benefits paid (86,871) (90,283)
Effect of changes in exchange rates and other (696) (2,501)
Balance at end of year 1,729,554 1,898,339
Japanese plans [Member] | Fair value of plan assets [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 2,128,476 1,840,586
Interest cost / income 29,462 21,377
Remeasurement    
Actual return on plan assets, excluding interest income (66,135) 266,101
Employer contributions 35,669 47,459
Plan participants' contributions 1,065 1,143
Benefits paid (47,528) (47,610)
Effect of changes in exchange rates and other   (579)
Balance at end of year 2,081,009 2,128,476
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 268,228  
Remeasurement    
Balance at end of year 572,107 268,228
Foreign plans [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 366,098  
Remeasurement    
Balance at end of year 350,817 366,098
Foreign plans [Member] | Present value of defined benefit obligations [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 1,651,016 1,423,263
Current service cost 49,225 45,581
Interest cost / income 81,411 73,014
Remeasurement    
Changes in demographic assumptions 68 1,337
Changes in financial assumptions (48,712) (16,818)
Other (15,579) 2,222
Past service cost (3,027) (18)
Plan participants' contributions 4,355 3,835
Benefits paid (76,204) (64,789)
Effect of changes in exchange rates and other (20,499) 183,389
Balance at end of year 1,622,053 1,651,016
Foreign plans [Member] | Fair value of plan assets [Member]    
Disclosure of defined benefit plans [line items]    
Balance at beginning of year 1,284,918 1,109,394
Interest cost / income 57,149 73,033
Remeasurement    
Actual return on plan assets, excluding interest income (33,874) (30,407)
Employer contributions 19,016 18,252
Plan participants' contributions 4,355 3,835
Benefits paid (42,023) (34,845)
Effect of changes in exchange rates and other (18,305) 145,656
Balance at end of year ¥ 1,271,236 ¥ 1,284,918