Transactions Involving Related Parties - Summary of Income Statement Impact of Transactions with Parent and Affiliated Companies (Detail) - USD ($) |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
|
| Revenue: | ||||
| Subsidy income | $ 2,669,000,000 | $ 2,412,000,000 | $ 7,927,000,000 | $ 7,000,000,000 |
| General and administrative expenses: | ||||
| Lease expense | 2,000,000 | 2,000,000 | 7,000,000 | 7,000,000 |
| Affiliated Entity | ||||
| Revenue: | ||||
| Subsidy income | 328,000,000 | 293,000,000 | 1,001,000,000 | 812,000,000 |
| General and administrative expenses: | ||||
| Support Compensation Agreement fees | 25,000,000 | 21,000,000 | 72,000,000 | 62,000,000 |
| Benefit plan expenses | 1,000,000 | 1,000,000 | 4,000,000 | 4,000,000 |
| Shared services | 20,000,000 | 19,000,000 | 59,000,000 | 58,000,000 |
| Lease expense | 1,000,000 | 1,000,000 | 3,000,000 | 3,000,000 |
| Related Party | ||||
| Interest expense: | ||||
| Related party debt | $ 0 | $ 0 | $ 28,000,000 | $ 0 |