Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
May 31, 2026 |
May 31, 2025 |
May 31, 2024 |
|
| Unrealized gains (losses) on securities, tax | $ 2.4 | $ 26.4 | $ 2.6 |
| Reclassification adjustment for realized gains (losses) on securities, tax | $ 1.9 | $ (0.1) | $ (0.7) |
| Dividends declared, per share | $ 4.43 | $ 4.02 | $ 3.65 |
| Authorized In July 2021 [Member] | |||
| Expiration date | Jan. 31, 2024 | Jan. 31, 2024 | Jan. 31, 2024 |
| Authorized In January 2026 [Member] | |||
| Repurchase authorization expired | $ 9.4 | $ 9.4 | $ 9.4 |
| Expiration date | Jan. 16, 2026 | Jan. 16, 2026 | Jan. 16, 2026 |
| Maximum [Member] | |||
| Approved repurchase amount | $ 1,000.0 | ||
| Maximum [Member] | Authorized In July 2021 [Member] | |||
| Approved repurchase amount | 400.0 | $ 400.0 | $ 400.0 |
| Maximum [Member] | Authorized In January 2026 [Member] | |||
| Approved repurchase amount | $ 400.0 | $ 400.0 | $ 400.0 |