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Liability for Future Policy Benefit, Activity (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Future Policy Benefits $ 36,806.4 $ 40,009.4    
Unum US        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year 2,431.4 2,071.1 $ 2,619.1  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 2,486.9 2,166.0 2,311.9  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   (58.7) 185.7 $ (97.1)
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (69.6) (90.2) (96.1)
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   2,358.6 2,261.5 2,118.7
Liability for Future Policy Benefit, Expected Net Premium, Issuance 485.0 486.5 304.8  
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 91.0 77.2 78.9  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected (368.6) (338.3) (336.4)  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 2,566.0 2,486.9 2,166.0  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax (123.3) (55.5) (94.9)  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 2,442.7 2,431.4 2,071.1  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 11,752.5 11,698.2 14,564.4  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 11,949.5 12,177.3 12,671.7  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   (197.2) 77.8 (228.2)
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (309.1) (377.2) (384.6)
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   11,443.2 11,877.9 12,058.9
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [1] 1,991.0 2,007.7 2,083.8  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 415.8 442.1 476.4  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (2,284.2) (2,378.2) (2,441.8)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 11,565.8 11,949.5 12,177.3  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (535.8) (197.0) (479.1)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 11,030.0 11,752.5 11,698.2  
Liability for Future Policy Benefit, before Reinsurance, before Other 8,587.3 9,321.1 9,627.1  
Liability for Future Policy Benefit, Other 30.4 31.6 41.6  
Liability for Future Policy Benefit, before Reinsurance, after Other 8,617.7 9,352.7 9,668.7  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 194.0 208.6 251.2  
Liability for Future Policy Benefit, after Reinsurance 8,423.7 9,144.1 9,417.5  
Gross premiums or assessments 6,547.1 6,263.2 6,021.7  
interest accretion 324.8 364.9 397.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 17,621.3 17,926.6 17,850.4  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 11,657.3 11,175.4 9,504.7  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 8,027.2 $ 7,830.4 $ 6,901.2  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 4.30% 4.20% 4.00%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 4.90% 4.50% 4.70%  
Liability for Future Policy Benefit, Weighted-Average Duration 7 years 1 month 6 days 7 years 6 years 9 months 18 days  
Future Policy Benefits [2] $ 8,617.7 $ 9,352.7 $ 9,668.7  
Unum International        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year 270.3 197.1 260.5  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 298.4 246.8 258.1  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   (5.9) (5.1) (0.3)
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   19.9 17.1 5.6
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   312.4 258.8 263.4
Liability for Future Policy Benefit, Expected Net Premium, Issuance 34.4 23.5 17.8  
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 11.4 9.4 8.4  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected (28.5) (23.0) (22.2)  
Liability for Future Policy Benefit, Expected Net Premium, Increase (Decrease) for Other Change (15.5) 29.7 (20.6)  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 314.2 298.4 246.8  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax (38.1) (28.1) (49.7)  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 276.1 270.3 197.1  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 2,527.4 2,231.4 3,181.8  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 2,687.1 2,495.5 2,703.8  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   0.1 17.7 (20.1)
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (20.5) 1.3 46.3
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   2,666.7 2,514.5 2,730.0
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [3] 379.0 335.2 327.7  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 67.9 63.5 64.9  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (409.3) (388.3) (346.7)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Increase (Decrease) for Other Change (62.8) 162.2 (280.4)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 2,641.5 2,687.1 2,495.5  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (249.9) (159.7) (264.1)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 2,391.6 2,527.4 2,231.4  
Liability for Future Policy Benefit, before Reinsurance, before Other 2,115.5 2,257.1 2,034.3  
Liability for Future Policy Benefit, Other 40.7 36.1 28.9  
Liability for Future Policy Benefit, before Reinsurance, after Other 2,156.2 2,293.2 2,063.2  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 67.9 78.7 70.3  
Liability for Future Policy Benefit, after Reinsurance 2,088.3 2,214.5 1,992.9  
Gross premiums or assessments 957.1 849.0 786.8  
interest accretion 56.5 54.1 56.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 4,258.2 4,261.1 3,905.4  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 1,295.7 1,196.6 943.9  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 823.4 $ 778.6 $ 626.2  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 4.10% 4.00% 4.00%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 5.10% 4.60% 5.00%  
Liability for Future Policy Benefit, Weighted-Average Duration 8 years 9 months 18 days 8 years 7 months 6 days 8 years 7 months 6 days  
Future Policy Benefits $ 2,156.2 $ 2,293.2 $ 2,063.2  
Colonial Life        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year 3,592.6 3,745.4 4,597.0  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 3,754.3 4,046.4 4,158.9  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   (7.9) (322.7) (32.3)
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (57.3) (53.5) (145.6)
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   3,689.1 3,670.2 3,981.0
Liability for Future Policy Benefit, Expected Net Premium, Issuance 555.9 544.9 554.9  
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 132.8 122.7 129.7  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected (584.0) (583.5) (619.2)  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 3,793.8 3,754.3 4,046.4  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax (240.5) (161.7) (301.0)  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 3,553.3 3,592.6 3,745.4  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 5,566.0 5,581.1 7,054.8  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 5,925.2 6,163.9 6,201.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   (52.7) (402.9) (85.9)
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (92.2) (52.0) (191.3)
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   5,780.3 5,709.0 5,924.3
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance 610.8 605.9 628.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 224.4 211.3 217.0  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (589.3) (601.0) (605.9)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 6,026.2 5,925.2 6,163.9  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (591.3) (359.2) (582.8)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 5,434.9 5,566.0 5,581.1  
Liability for Future Policy Benefit, before Reinsurance, before Other 1,881.6 1,973.4 1,835.7  
Liability for Future Policy Benefit, Other 22.6 24.4 22.7  
Liability for Future Policy Benefit, before Reinsurance, after Other 1,904.2 1,997.8 1,858.4  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 0.9 1.8 1.1  
Liability for Future Policy Benefit, after Reinsurance 1,903.3 1,996.0 1,857.3  
Gross premiums or assessments 1,718.9 1,658.6 1,635.8  
interest accretion 91.6 88.6 87.3  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 10,409.4 9,796.7 10,011.9  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 12,618.4 11,903.1 12,221.3  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 9,049.4 $ 8,702.2 $ 8,966.3  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 4.40% 4.30% 4.30%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 5.50% 4.80% 5.20%  
Liability for Future Policy Benefit, Weighted-Average Duration 17 years 3 months 18 days 17 years 17 years 6 months  
Future Policy Benefits $ 1,904.2 $ 1,997.8 $ 1,858.4  
Closed Block        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year 8,123.5 6,412.6 8,404.7  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 7,703.6 6,236.1 6,457.3  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   145.5 1,641.3 27.8
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (41.2) 44.1 (33.5)
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   7,807.9 7,921.5 6,451.6
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 401.8 374.7 349.0  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected (616.8) (592.6) (564.5)  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 7,592.9 7,703.6 6,236.1  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax 65.6 419.9 176.5  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 7,658.5 8,123.5 6,412.6  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 32,577.7 29,418.7 40,504.0  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 30,743.9 28,852.3 28,820.2  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   1.3 2,009.4 241.8
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   85.7 117.1 (5.5)
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   30,830.9 30,978.8 29,056.5
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [4] 101.2 123.4 154.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 1,545.0 1,510.3 1,477.9  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (1,932.4) (1,868.6) (1,836.6)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 30,544.7 30,743.9 28,852.3  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (481.1) 1,833.8 566.4  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 30,063.6 32,577.7 29,418.7  
Liability for Future Policy Benefit, before Reinsurance, before Other 22,405.1 24,454.2 23,006.1  
Liability for Future Policy Benefit, Other [5] 1,498.0 1,661.2 1,761.3  
Liability for Future Policy Benefit, before Reinsurance, after Other 23,903.1 26,115.4 24,767.4  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 6,775.9 7,466.9 7,805.5  
Liability for Future Policy Benefit, after Reinsurance 17,127.2 18,648.5 16,961.9  
Gross premiums or assessments 884.4 919.9 947.5  
interest accretion 1,143.2 1,135.6 1,128.9  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 71,145.2 73,341.4 65,293.0  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 13,767.1 14,486.4 12,629.9  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 8,029.1 $ 8,241.7 $ 7,333.5  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 5.30% 5.20% 5.20%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 5.50% 4.90% 5.20%  
Liability for Future Policy Benefit, Weighted-Average Duration 12 years 10 months 24 days 13 years 2 months 12 days 12 years 4 months 24 days  
Future Policy Benefits [2] $ 23,903.1 $ 26,115.4 $ 24,767.4  
Other Products        
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Future Policy Benefits [2] 225.2 250.3 219.4  
Group Disability | Unum US        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   0.0 0.0 0.0
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   0.0 0.0 0.0
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   0.0 0.0 0.0
Liability for Future Policy Benefit, Expected Net Premium, Issuance 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 0.0 0.0 0.0  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 5,147.4 5,533.3 6,725.7  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 5,277.1 5,793.1 6,158.3  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   (76.4) (100.2) (102.0)
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (168.9) (204.0) (239.4)
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   5,031.8 5,488.9 5,816.9
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [1] 1,093.2 1,094.5 1,304.3  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 151.3 171.2 210.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (1,368.8) (1,477.5) (1,538.6)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 4,907.5 5,277.1 5,793.1  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (171.7) (129.7) (259.8)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 4,735.8 5,147.4 5,533.3  
Liability for Future Policy Benefit, before Reinsurance, before Other 4,735.8 5,147.4 5,533.3  
Liability for Future Policy Benefit, Other 0.4 0.2 0.4  
Liability for Future Policy Benefit, before Reinsurance, after Other 4,736.2 5,147.6 5,533.7  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 26.4 30.7 36.0  
Liability for Future Policy Benefit, after Reinsurance 4,709.8 5,116.9 5,497.7  
Gross premiums or assessments 3,070.4 2,958.7 2,791.7  
interest accretion 151.3 171.2 210.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 5,953.3 6,376.6 6,988.1  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 0.0 $ 0.0 $ 0.0  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 4.20% 4.00% 3.80%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 4.90% 4.60% 4.90%  
Liability for Future Policy Benefit, Weighted-Average Duration 4 years 2 months 12 days 4 years 3 months 18 days 4 years 4 months 24 days  
Group Life and AD&D | Unum US        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year $ 0.0 $ 0.0 $ 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   0.0 0.0 0.0
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   0.0 0.0 0.0
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   0.0 0.0 0.0
Liability for Future Policy Benefit, Expected Net Premium, Issuance 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 0.0 0.0 0.0  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 922.0 972.6 1,124.1  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 936.5 998.5 1,058.3  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   (17.0) 0.0 (32.9)
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (53.1) (37.0) (34.3)
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   866.4 961.5 991.1
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [1] 375.4 394.2 444.1  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 17.7 20.0 24.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (406.9) (439.2) (461.2)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 852.6 936.5 998.5  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (17.4) (14.5) (25.9)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 835.2 922.0 972.6  
Liability for Future Policy Benefit, before Reinsurance, before Other 835.2 922.0 972.6  
Liability for Future Policy Benefit, Other 0.8 1.0 0.9  
Liability for Future Policy Benefit, before Reinsurance, after Other 836.0 923.0 973.5  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 5.3 7.2 7.5  
Liability for Future Policy Benefit, after Reinsurance 830.7 915.8 966.0  
Gross premiums or assessments 1,996.0 1,878.0 1,864.9  
interest accretion 17.7 20.0 24.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 964.5 1,063.2 1,133.0  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 0.0 $ 0.0 $ 0.0  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 2.30% 2.20% 2.20%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 2.70% 2.60% 2.70%  
Liability for Future Policy Benefit, Weighted-Average Duration 2 years 4 months 24 days 2 years 7 months 6 days 2 years 7 months 6 days  
Voluntary Benefits | Unum US        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year $ 1,134.7 $ 868.2 $ 1,124.8  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 1,192.5 937.9 1,032.3  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   41.5 180.7 (23.4)
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (66.2) (79.8) (70.9)
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   1,167.8 1,038.8 938.0
Liability for Future Policy Benefit, Expected Net Premium, Issuance 316.3 288.6 136.2  
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 39.4 29.0 29.1  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected (188.2) (163.9) (165.4)  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 1,335.3 1,192.5 937.9  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax (95.1) (57.8) (69.7)  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 1,240.2 1,134.7 868.2  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 2,334.5 1,999.5 2,697.3  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 2,422.0 2,141.2 2,201.8  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   51.6 170.1 (39.9)
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (68.0) (90.9) (74.9)
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   2,405.6 2,220.4 2,087.0
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [1] 339.3 303.7 154.0  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 97.7 86.2 86.1  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (228.0) (188.3) (185.9)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 2,614.6 2,422.0 2,141.2  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (252.1) (87.5) (141.7)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 2,362.5 2,334.5 1,999.5  
Liability for Future Policy Benefit, before Reinsurance, before Other 1,122.3 1,199.8 1,131.3  
Liability for Future Policy Benefit, Other 2.8 2.6 15.6  
Liability for Future Policy Benefit, before Reinsurance, after Other 1,125.1 1,202.4 1,146.9  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 13.0 14.0 14.1  
Liability for Future Policy Benefit, after Reinsurance 1,112.1 1,188.4 1,132.8  
Gross premiums or assessments 821.7 789.9 773.6  
interest accretion 58.3 57.2 57.0  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 5,590.6 5,173.1 4,561.1  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 5,799.1 5,450.6 3,979.6  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 3,815.4 $ 3,717.5 $ 2,939.1  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 5.00% 5.00% 5.10%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 5.50% 4.90% 5.20%  
Liability for Future Policy Benefit, Weighted-Average Duration 18 years 3 months 18 days 18 years 1 month 6 days 17 years 9 months 18 days  
Individual Disability | Unum US        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year $ 1,296.7 $ 1,202.9 $ 1,494.3  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 1,294.4 1,228.1 1,279.6  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   (100.2) 5.0 (73.7)
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (3.4) (10.4) (25.2)
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   1,190.8 1,222.7 1,180.7
Liability for Future Policy Benefit, Expected Net Premium, Issuance 168.7 197.9 168.6  
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 51.6 48.2 49.8  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected (180.4) (174.4) (171.0)  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 1,230.7 1,294.4 1,228.1  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax (28.2) 2.3 (25.2)  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 1,202.5 1,296.7 1,202.9  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 3,348.6 3,192.8 4,017.3  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 3,313.9 3,244.5 3,253.3  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   (155.4) 7.9 (53.4)
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (19.1) (45.3) (36.0)
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   3,139.4 3,207.1 3,163.9
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [1] 183.1 215.3 181.4  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 149.1 164.7 155.3  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (280.5) (273.2) (256.1)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 3,191.1 3,313.9 3,244.5  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (94.6) 34.7 (51.7)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 3,096.5 3,348.6 3,192.8  
Liability for Future Policy Benefit, before Reinsurance, before Other 1,894.0 2,051.9 1,989.9  
Liability for Future Policy Benefit, Other 26.4 27.8 24.7  
Liability for Future Policy Benefit, before Reinsurance, after Other 1,920.4 2,079.7 2,014.6  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 149.3 156.7 193.6  
Liability for Future Policy Benefit, after Reinsurance 1,771.1 1,923.0 1,821.0  
Gross premiums or assessments 659.0 636.6 591.5  
interest accretion 97.5 116.5 105.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 5,112.9 5,313.7 5,168.2  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 5,858.2 5,724.8 5,525.1  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 4,211.8 $ 4,112.9 $ 3,962.1  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 5.10% 5.10% 5.10%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 5.30% 4.80% 5.10%  
Liability for Future Policy Benefit, Weighted-Average Duration 9 years 4 months 24 days 9 years 7 months 6 days 9 years 4 months 24 days  
Long-term Care | Closed Block        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year $ 8,123.5 $ 6,412.6 $ 8,404.7  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 7,703.6 6,236.1 6,457.3  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   145.5 1,641.3 27.8
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (41.2) 44.1 (33.5)
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   7,807.9 7,921.5 6,451.6
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 401.8 374.7 349.0  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected (616.8) (592.6) (564.5)  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 7,592.9 7,703.6 6,236.1  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax 65.6 419.9 176.5  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 7,658.5 8,123.5 6,412.6  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 24,697.7 21,199.9 30,089.6  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 22,649.3 20,221.6 19,870.8  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   (4.1) 2,009.4 24.9
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   68.3 113.1 (36.2)
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   22,713.5 22,344.1 19,859.5
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [4] 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 1,199.8 1,151.4 1,105.1  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (959.6) (846.2) (743.0)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 22,953.7 22,649.3 20,221.6  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (28.5) 2,048.4 978.3  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 22,925.2 24,697.7 21,199.9  
Liability for Future Policy Benefit, before Reinsurance, before Other 15,266.7 16,574.2 14,787.3  
Liability for Future Policy Benefit, Other [5] 1.7 23.1 24.3  
Liability for Future Policy Benefit, before Reinsurance, after Other 15,268.4 16,597.3 14,811.6  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 4.2 4.5 5.7  
Liability for Future Policy Benefit, after Reinsurance 15,264.2 16,592.8 14,805.9  
Gross premiums or assessments 696.2 696.1 697.5  
interest accretion 798.0 776.7 756.1  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 60,051.5 61,447.7 52,544.0  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 13,767.1 14,486.4 12,629.9  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 8,029.1 $ 8,241.7 $ 7,333.5  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 5.60% 5.60% 5.50%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 5.60% 5.00% 5.20%  
Liability for Future Policy Benefit, Weighted-Average Duration 15 years 8 months 12 days 16 years 4 months 24 days 15 years 6 months  
Other Insurance Product Line | Closed Block        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year $ 0.0 $ 0.0 $ 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   0.0 0.0 0.0
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   0.0 0.0 0.0
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   0.0 0.0 0.0
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 0.0 0.0 0.0  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 7,880.0 8,218.8 10,414.4  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 8,094.6 8,630.7 8,949.4  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   5.4 0.0 216.9
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   17.4 4.0 30.7
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   8,117.4 8,634.7 9,197.0
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [4] 101.2 123.4 154.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 345.2 358.9 372.8  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (972.8) (1,022.4) (1,093.6)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 7,591.0 8,094.6 8,630.7  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (452.6) (214.6) (411.9)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 7,138.4 7,880.0 8,218.8  
Liability for Future Policy Benefit, before Reinsurance, before Other 7,138.4 7,880.0 8,218.8  
Liability for Future Policy Benefit, Other [5] 1,496.3 1,638.1 1,737.0  
Liability for Future Policy Benefit, before Reinsurance, after Other 8,634.7 9,518.1 9,955.8  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 6,771.7 7,462.4 7,799.8  
Liability for Future Policy Benefit, after Reinsurance 1,863.0 2,055.7 2,156.0  
Gross premiums or assessments 188.2 223.8 250.0  
interest accretion 345.2 358.9 372.8  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 11,093.7 11,893.7 12,749.0  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 0.0 0.0 0.0  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 0.0 $ 0.0 $ 0.0  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 4.60% 4.60% 4.60%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 5.40% 4.90% 5.10%  
Liability for Future Policy Benefit, Weighted-Average Duration 7 years 2 months 12 days 7 years 3 months 18 days 7 years 4 months 24 days  
Operating Segments        
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]        
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance beginning of year $ 14,417.8 $ 12,426.2 $ 15,881.3  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance beginning of year 14,243.2 12,695.3 13,186.2  
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) from Cash Flow Change   73.0 1,499.2 (101.9)
Liability for Future Policy Benefit, Expected Net Premium, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (148.2) (82.5) (269.6)
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Reinsurance, after Cash Flow Change   14,168.0 14,112.0 12,814.7
Liability for Future Policy Benefit, Expected Net Premium, Issuance 1,075.3 1,054.9 877.5  
Liability for Future Policy Benefit, Expected Net Premium, Interest Income 637.0 584.0 566.0  
Liability for Future Policy Benefit, Expected Net Premium, Net Premium Collected (1,597.9) (1,537.4) (1,542.3)  
Liability for Future Policy Benefit, Expected Net Premium, Increase (Decrease) for Other Change (15.5) 29.7 (20.6)  
Liability for Future Policy Benefit, Expected Net Premium, Original Discount Rate, before Cash Flow and Reinsurance, balance end of period 14,266.9 14,243.2 12,695.3  
AOCI, Liability for Future Policy Benefit, Expected Net Premium, before Tax (336.3) 174.6 (269.1)  
Liability for Future Policy Benefit, Expected Net Premium, before Reinsurance, after Discount Rate Change, balance end of period 13,930.6 14,417.8 12,426.2  
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]        
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance beginning of year 52,423.6 48,929.4 65,305.0  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at beginning of year 51,305.7 49,689.0 50,397.2  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change   (248.5) 1,702.0 (92.4)
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) of Actual Variance from Expected Experience   (336.1) (310.8) (535.1)
Liability for Future Policy Benefit, Expected Future Benefit, Original Discount Rate, before Reinsurance, after Cash Flow Change   50,721.1 51,080.2 $ 49,769.7
Liability for Future Policy Benefit, Expected Future Policy Benefit, Issuance [6] 3,082.0 3,072.2 3,194.5  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Interest Expense 2,253.1 2,227.2 2,236.2  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment (5,215.2) (5,236.1) (5,231.0)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Increase (Decrease) for Other Change (62.8) 162.2 (280.4)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Original Discount Rate, before Cash Flow and Reinsurance, balance at end of period 50,778.2 51,305.7 49,689.0  
AOCI, Liability for Future Policy Benefit, Expected Future Policy Benefit, before Tax (1,858.1) 1,117.9 (759.6)  
Liability for Future Policy Benefit, Expected Future Policy Benefit, before Reinsurance, after Discount Rate Change, balance end of period 48,920.1 52,423.6 48,929.4  
Liability for Future Policy Benefit, before Reinsurance, before Other 34,989.5 38,005.8 36,503.2  
Liability for Future Policy Benefit, Other [7] 1,591.7 1,753.3 1,854.5  
Liability for Future Policy Benefit, before Reinsurance, after Other 36,581.2 39,759.1 38,357.7  
Liability for Future Policy Benefit, Reinsurance Recoverable, after Allowance 7,038.7 7,756.1 8,128.2  
Liability for Future Policy Benefit, after Reinsurance 29,542.5 32,003.0 30,229.5  
Gross premiums or assessments 10,107.5 9,690.7 9,391.8  
interest accretion 1,616.1 1,643.2 1,670.2  
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted, before Reinsurance 103,434.1 105,325.8 97,060.7  
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance 39,338.5 38,761.5 35,299.8  
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance $ 25,929.1 $ 25,552.9 $ 23,827.2  
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate 4.90% 4.80% 4.80%  
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate 5.30% 4.80% 5.00%  
Liability for Future Policy Benefit, Weighted-Average Duration 11 years 4 months 24 days 11 years 6 months 10 years 10 months 24 days  
Future Policy Benefits $ 36,806.4 $ 40,009.4 $ 38,577.1  
[1]
1Issuances include new policy issuances for most product lines. Issuances for Unum US group disability and Unum US group life and AD&D represents new claim incurrals.
[2]
1Unum US excludes the dental and vision product line and medical stop-loss products and Closed Block excludes our participating fund account, which represents policies issued by one of our subsidiaries prior to its 1986 conversion from a mutual stock life insurance company. The liabilities associated with these products are included within Other products.
[3]
1Issuances for Unum International primarily represent new claim incurrals.
[4]
1Issuances for Closed Block - All Other represents new claim incurrals.
[5]
2Other for Closed Block - All Other primarily includes our closed block group pension products and certain of our ceded closed block individual life products.
[6]
1Issuances include new policy issuances for most product lines. For our Unum US group disability, Unum US group life and AD&D and Closed Block - All Other product lines and certain of our Unum International product lines, this line represents new claim incurrals.
[7]
2Other primarily relates to our Closed Block - All Other product line.