Treasury Stock Transactions (Details) - USD ($) shares in Millions, $ in Millions |
1 Months Ended | 3 Months Ended | 6 Months Ended | 8 Months Ended | 9 Months Ended | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Feb. 28, 2025 |
[3] | Nov. 30, 2024 |
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Dec. 31, 2025 |
Nov. 01, 2024 |
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| Equity, Class of Treasury Stock | ||||||||||||||||||||
| Cost of Shares Repurchased | [1] | $ 202.1 | $ 303.3 | $ 604.5 | $ 505.9 | |||||||||||||||
| Number of Treasury Shares Repurchased | [2] | 2.5 | 3.8 | 7.9 | 7.1 | |||||||||||||||
| Commissions Paid on Stock Repurchases | $ 0.2 | $ 0.4 | $ 0.3 | $ 0.9 | ||||||||||||||||
| Share Repurchases Excise Tax | 2.0 | $ 2.9 | $ 5.7 | $ 5.0 | ||||||||||||||||
| Accelerated Share Repurchases, Cash or Stock Settlement | Under the terms of the agreements, we are to receive, or be required to pay, a price adjustment based on the volume weighted average price of Unum Group common stock during the term of the agreement, less a discount. Any price adjustment payable to us is settled in shares of Unum Group common stock. Any price adjustment we would be required to pay may be settled in either cash or common stock at our option. | |||||||||||||||||||
| November 2024 Accelerated Share Repurchase | ||||||||||||||||||||
| Equity, Class of Treasury Stock | ||||||||||||||||||||
| Number of Treasury Shares Repurchased | 0.7 | 3.8 | ||||||||||||||||||
| ASR prepayment amount | [3] | $ 321.0 | ||||||||||||||||||
| Repurchase Program Authorized in July 2024 | ||||||||||||||||||||
| Equity, Class of Treasury Stock | ||||||||||||||||||||
| Share Repurchase Program, Expiration Date | [4] | Mar. 31, 2025 | ||||||||||||||||||
| Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program | [4] | 1,000.0 | $ 1,000.0 | |||||||||||||||||
| Cost of Shares Repurchased | [4] | $ 706.8 | ||||||||||||||||||
| Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program | [4] | 0.0 | $ 0.0 | |||||||||||||||||
| Repurchase Program Authorized in February 2025 | ||||||||||||||||||||
| Equity, Class of Treasury Stock | ||||||||||||||||||||
| Share Repurchase Program, Expiration Date | [5] | Dec. 31, 2025 | ||||||||||||||||||
| Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program | [5] | 1,000.0 | $ 1,000.0 | |||||||||||||||||
| Cost of Shares Repurchased | [5] | $ 800.0 | ||||||||||||||||||
| Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program | [5] | 0.0 | 0.0 | |||||||||||||||||
| Repurchase Program Authorized in December 2025 | ||||||||||||||||||||
| Equity, Class of Treasury Stock | ||||||||||||||||||||
| Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program | 1,000.0 | 1,000.0 | ||||||||||||||||||
| Cost of Shares Repurchased | 598.5 | |||||||||||||||||||
| Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program | $ 401.5 | $ 401.5 | ||||||||||||||||||
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