v3.26.3
Accumulated Other Comprehensive Income (Loss) (Changes in Components of Accumulated Other Comprehensive Income (Loss)) (Detail) - JPY (¥)
¥ in Millions
 6 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Accumulated Other Comprehensive Income (Loss) [Line Items]    
Beginning Balance ¥ 4,573,068 ¥ 4,171,783
Total other comprehensive income (loss) (32,115) 217,046
Ending Balance 5,171,623 4,521,858
Net unrealized gains (losses) on investment in securities    
Accumulated Other Comprehensive Income (Loss) [Line Items]    
Beginning Balance (618,351) (403,914)
Net unrealized gains (losses) (103,812) (83,351)
Reclassification adjustment included in net income, net of tax (8,207) (4,714)
Total other comprehensive income (loss) (112,019) (88,065)
Transaction with noncontrolling interests 0 0
Less: Other Comprehensive Income (Loss) Attributable to the Noncontrolling Interests 0 0
Less: Other Comprehensive Income (Loss) Attributable to the Redeemable Noncontrolling Interests (6) (6)
Ending Balance (730,364) [1] (491,973) [2]
Impact of changes in policy liability discount rate    
Accumulated Other Comprehensive Income (Loss) [Line Items]    
Beginning Balance 715,382 416,124
Net unrealized gains (losses) 83,880 311,459
Total other comprehensive income (loss) 83,880 311,459
Transaction with noncontrolling interests 0 0
Less: Other Comprehensive Income (Loss) Attributable to the Noncontrolling Interests 0 0
Less: Other Comprehensive Income (Loss) Attributable to the Redeemable Noncontrolling Interests 0 0
Ending Balance 799,262 [1] 727,583 [2]
Debt Valuation Adjustments    
Accumulated Other Comprehensive Income (Loss) [Line Items]    
Beginning Balance 242 49
Net unrealized gains (losses) 34 192
Reclassification adjustment included in net income, net of tax (4) (4)
Total other comprehensive income (loss) 30 188
Transaction with noncontrolling interests 0 0
Less: Other Comprehensive Income (Loss) Attributable to the Noncontrolling Interests 0 0
Less: Other Comprehensive Income (Loss) Attributable to the Redeemable Noncontrolling Interests 0 0
Ending Balance 272 [1] 237 [2]
Defined benefit pension plans    
Accumulated Other Comprehensive Income (Loss) [Line Items]    
Beginning Balance 31,953 14,791
Net unrealized gains (losses) 9,055 5,716
Reclassification adjustment included in net income, net of tax (377) (171)
Total other comprehensive income (loss) 8,678 5,545
Transaction with noncontrolling interests 0 0
Less: Other Comprehensive Income (Loss) Attributable to the Noncontrolling Interests (12) (3)
Less: Other Comprehensive Income (Loss) Attributable to the Redeemable Noncontrolling Interests 0 0
Ending Balance 40,643 [1] 20,339 [2]
Foreign currency translation adjustments    
Accumulated Other Comprehensive Income (Loss) [Line Items]    
Beginning Balance 469,262 304,657
Net unrealized gains (losses) (18,250) 1,701
Reclassification adjustment included in net income, net of tax 2,158 (6,689)
Total other comprehensive income (loss) (16,092) (4,988)
Transaction with noncontrolling interests 0 28
Less: Other Comprehensive Income (Loss) Attributable to the Noncontrolling Interests (145) (614)
Less: Other Comprehensive Income (Loss) Attributable to the Redeemable Noncontrolling Interests (822) 402
Ending Balance 454,137 [1] 299,909 [2]
Net unrealized gains (losses) on derivative instruments    
Accumulated Other Comprehensive Income (Loss) [Line Items]    
Beginning Balance 6,622 9,591
Net unrealized gains (losses) (1,726) (3,585)
Reclassification adjustment included in net income, net of tax 5,134 (3,508)
Total other comprehensive income (loss) 3,408 (7,093)
Transaction with noncontrolling interests 0 0
Less: Other Comprehensive Income (Loss) Attributable to the Noncontrolling Interests 100 (31)
Less: Other Comprehensive Income (Loss) Attributable to the Redeemable Noncontrolling Interests 0 0
Ending Balance 9,930 [1] 2,529 [2]
AOCI Attributable to Parent    
Accumulated Other Comprehensive Income (Loss) [Line Items]    
Beginning Balance 605,110 341,298
Total other comprehensive income (loss) (32,115) 217,046
Transaction with noncontrolling interests 0 28
Less: Other Comprehensive Income (Loss) Attributable to the Noncontrolling Interests (57) (648)
Less: Other Comprehensive Income (Loss) Attributable to the Redeemable Noncontrolling Interests (828) 396
Ending Balance ¥ 573,880 [1] ¥ 558,624 [2]
[1] As of September 30, 2026, net unrealized gains (losses) on investment in securities contained ¥(145) million (net of tax of ¥47 million) of net unrealized gains (losses) on investment in securities related to available-for-sale debt securities with allowance for credit losses.
[2] As of September 30, 2025, net unrealized gains (losses) on investment in securities contained ¥(186) million (net of tax of ¥28 million ) of net unrealized gains (losses) on investment in securities related to available-for-sale debt securities with allowance for credit losses.