v3.26.1
Transactions Involving Related Parties - Summary of Income Statement Impact of Transactions with Parent and Affiliated Companies (Detail) - USD ($)
3 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Revenue:    
Subsidy income $ 2,720,000,000 $ 2,598,000,000
General and administrative expenses:    
Lease expense 2,000,000 2,000,000
Affiliated Entity    
Revenue:    
Subsidy income 350,000,000 338,000,000
General and administrative expenses:    
Support Compensation Agreement fees 24,000,000 23,000,000
Benefit plan expenses 1,000,000 2,000,000
Shared services 19,000,000 19,000,000
Lease expense 1,000,000 1,000,000
Related Party    
Interest expense:    
Related party debt $ 0 $ 20,000,000