XML 44 R33.htm IDEA: XBRL DOCUMENT v3.25.3
Fair Value Measurements by Input Level (Detail) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Assets, Fair Value Disclosure    
Fixed Maturity Securities $ 33,190.2 $ 35,629.9
Equity Securities 23.2 24.5
Other Long-term Investments $ 1,682.2 $ 1,694.4
Derivative Asset, Statement of Financial Position [Extensible Enumeration] Other Long-term Investments Other Long-term Investments
Derivative Assets $ 70.5 $ 90.9
Assets, Fair Value Disclosure $ 34,740.2 $ 37,195.9
Liabilities    
Derivative Liability, Statement of Financial Position [Extensible Enumeration] Other Liabilities Other Liabilities
Derivative Liabilities $ 259.6 $ 255.7
Liabilities, Fair Value Disclosure 259.6 255.7
Forwards    
Assets, Fair Value Disclosure    
Derivative Assets 5.0 6.5
Liabilities    
Derivative Liabilities 208.2 223.2
Interest Rate Swaps    
Assets, Fair Value Disclosure    
Derivative Assets 51.6 72.9
Liabilities    
Derivative Liabilities 51.4 32.5
Embedded Derivative in Modified Coinsurance Arrangement    
Assets, Fair Value Disclosure    
Derivative Assets 13.9 11.5
Fair Value, Measurements, Recurring    
Assets, Fair Value Disclosure    
Other Long-term Investments 1,550.0 1,566.0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 6,711.8 4,180.5
Equity Securities 0.0 0.0
Other Long-term Investments 0.0 0.0
Assets, Fair Value Disclosure 6,711.8 4,180.5
Liabilities    
Liabilities, Fair Value Disclosure 0.0 0.0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 26,335.4 31,304.4
Equity Securities 0.2 0.1
Other Long-term Investments 56.8 79.5
Derivative Assets 56.6 79.4
Assets, Fair Value Disclosure 26,392.2 31,383.9
Liabilities    
Derivative Liabilities 259.6 255.7
Liabilities, Fair Value Disclosure 259.6 255.7
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Forwards    
Assets, Fair Value Disclosure    
Derivative Assets 5.0 6.5
Liabilities    
Derivative Liabilities 208.2 223.2
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Interest Rate Swaps    
Assets, Fair Value Disclosure    
Derivative Assets 51.6 72.9
Liabilities    
Derivative Liabilities 51.4 32.5
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 143.0 145.0
Equity Securities 23.0 24.4
Other Long-term Investments 36.9 35.9
Derivative Assets 13.9 11.5
Assets, Fair Value Disclosure 179.9 180.9
Liabilities    
Liabilities, Fair Value Disclosure 0.0 0.0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Embedded Derivative in Modified Coinsurance Arrangement    
Assets, Fair Value Disclosure    
Derivative Assets 13.9 11.5
Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Equity Securities 0.0 0.0
Other Long-term Investments 1,456.3 1,450.6
Assets, Fair Value Disclosure 1,456.3 1,450.6
Liabilities    
Liabilities, Fair Value Disclosure 0.0 0.0
United States Government and Government Agencies and Authorities    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 544.0 530.5
United States Government and Government Agencies and Authorities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 79.7 77.9
United States Government and Government Agencies and Authorities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 464.3 452.6
United States Government and Government Agencies and Authorities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
United States Government and Government Agencies and Authorities | Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
States, Municipalities, and Political Subdivisions    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 3,068.0 3,291.4
States, Municipalities, and Political Subdivisions | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
States, Municipalities, and Political Subdivisions | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 3,068.0 3,291.4
States, Municipalities, and Political Subdivisions | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
States, Municipalities, and Political Subdivisions | Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Foreign Governments    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 879.5 768.1
Foreign Governments | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Foreign Governments | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 879.5 768.1
Foreign Governments | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Foreign Governments | Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Public Utilities    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 4,888.8 5,292.9
Public Utilities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 471.6 174.5
Public Utilities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 4,417.2 5,118.4
Public Utilities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Public Utilities | Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Mortgage/Asset-backed Securities    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 1,121.6 [1] 917.2 [2]
Mortgage/Asset-backed Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1    
Assets, Fair Value Disclosure    
Fixed Maturity Securities [1] 0.0 0.0
Mortgage/Asset-backed Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2    
Assets, Fair Value Disclosure    
Fixed Maturity Securities [1] 1,022.6 843.7
Mortgage/Asset-backed Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3    
Assets, Fair Value Disclosure    
Fixed Maturity Securities [1] 99.0 73.5
Mortgage/Asset-backed Securities | Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share    
Assets, Fair Value Disclosure    
Fixed Maturity Securities [1] 0.0 0.0
All Other Corporate Bonds    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 22,680.5 24,822.2
All Other Corporate Bonds | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 6,160.5 3,928.1
All Other Corporate Bonds | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 16,476.0 20,822.6
All Other Corporate Bonds | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 44.0 71.5
All Other Corporate Bonds | Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Redeemable Preferred Stocks    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 7.8 7.6
Redeemable Preferred Stocks | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Redeemable Preferred Stocks | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 7.8 7.6
Redeemable Preferred Stocks | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Redeemable Preferred Stocks | Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share    
Assets, Fair Value Disclosure    
Fixed Maturity Securities 0.0 0.0
Private Equity Partnerships    
Assets, Fair Value Disclosure    
Alternative Investments 1,456.3 1,450.6
Private Equity Partnerships | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1    
Assets, Fair Value Disclosure    
Alternative Investments 0.0 0.0
Private Equity Partnerships | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2    
Assets, Fair Value Disclosure    
Alternative Investments 0.0 0.0
Private Equity Partnerships | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3    
Assets, Fair Value Disclosure    
Alternative Investments 0.0 0.0
Private Equity Partnerships | Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share    
Assets, Fair Value Disclosure    
Alternative Investments $ 1,456.3 $ 1,450.6
[1]
1Includes credit-tranched securities collateralized by loan obligations, auto loans, and other asset types
[2]
1Includes credit-tranched securities collateralized by loan obligations, auto loans, and other asset types