v3.26.1
Contents of Significant Accounts - Movements in Present Value of Defined Benefit Obligation and Fair Value of Plan Assets (Detail) - TWD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Present value of defined benefit obligation [member]    
Disclosure of net defined benefit liability (asset) [line items]    
Beginning balance $ (4,392,723) $ (4,665,498)
Service cost (5,749) (8,435)
Interest income (cost) (69,844) (55,986)
Subtotal (75,593) (64,421)
Arising from changes in demographic assumptions 0 (142,117)
Arising from changes in financial assumptions (80,095) 98,669
Experience adjustments 28,043 20,669
Subtotal (52,052) (22,779)
Benefits paid 269,846 359,975
Ending balance (4,250,522) (4,392,723)
Plan assets [member]    
Disclosure of net defined benefit liability (asset) [line items]    
Beginning balance 2,960,474 2,460,413
Interest income (cost) 47,071 29,525
Contribution by employer 449,449 619,281
Benefits paid (269,846) (359,975)
Return on plan assets, excluding amounts included in interest income 197,155 211,230
Ending balance $ 3,384,303 $ 2,960,474