Postretirement Benefit Plans (Employer Contributions to Plans) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Mar. 31, 2025 |
Mar. 31, 2024 |
Mar. 31, 2023 |
|
| Contributions to employee benefit plans | |||
| Funded pension plans | $ 39 | $ 30 | $ 22 |
| Unfunded pension plans | 17 | 17 | 15 |
| Savings and defined contribution pension plans | 62 | 59 | 54 |
| Total contributions | 118 | 106 | 91 |
| Defined Benefit Plan Disclosure [Line Items] | |||
| Payment for Pension and Other Postretirement Benefits | 118 | $ 106 | $ 91 |
| Additional Contributions To Funded Pension Plan | 24 | ||
| Additional Contributions To Unfunded Pension Plan | 18 | ||
| Employer discretionary contribution amount | $ 63 | ||