INVESTMENTS - Gross Unrealized Losses On Fixed Maturity Securities (Details) $ in Millions	Dec. 31, 2021 USD ($)
Fair Value
Less Than Twelve Months	$ 3,515.0
Twelve Months or More	285.0
Total	3,800.0
Gross   Unrealized  Losses
Less Than Twelve Months	74.0
Twelve Months or More	11.0
Total	85.0
U.S Treasury securities and obligations of U.S. government authorities and agencies
Fair Value
Less Than Twelve Months	74.0
Twelve Months or More	0.0
Total	74.0
Gross   Unrealized  Losses
Less Than Twelve Months	1.0
Twelve Months or More	0.0
Total	1.0
Obligations of U.S. states and their political subdivisions
Fair Value
Less Than Twelve Months	5.0
Twelve Months or More	0.0
Total	5.0
Gross   Unrealized  Losses
Less Than Twelve Months	0.0
Twelve Months or More	0.0
Total	0.0
Foreign government bonds
Fair Value
Less Than Twelve Months	13.0
Twelve Months or More	7.0
Total	20.0
Gross   Unrealized  Losses
Less Than Twelve Months	1.0
Twelve Months or More	0.0
Total	1.0
U.S. corporate public securities
Fair Value
Less Than Twelve Months	696.0
Twelve Months or More	153.0
Total	849.0
Gross   Unrealized  Losses
Less Than Twelve Months	11.0
Twelve Months or More	6.0
Total	18.0
U.S. corporate private securities
Fair Value
Less Than Twelve Months	855.0
Twelve Months or More	0.0
Total	855.0
Gross   Unrealized  Losses
Less Than Twelve Months	14.0
Twelve Months or More	0.0
Total	14.0
Foreign corporate public securities
Fair Value
Less Than Twelve Months	522.0
Twelve Months or More	50.0
Total	572.0
Gross   Unrealized  Losses
Less Than Twelve Months	8.0
Twelve Months or More	1.0
Total	9.0
Foreign corporate private securities
Fair Value
Less Than Twelve Months	689.0
Twelve Months or More	0.0
Total	689.0
Gross   Unrealized  Losses
Less Than Twelve Months	34.0
Twelve Months or More	0.0
Total	34.0
Asset-backed securities
Fair Value
Less Than Twelve Months	499.0
Twelve Months or More	0.0
Total	499.0
Gross   Unrealized  Losses
Less Than Twelve Months	1.0
Twelve Months or More	0.0
Total	1.0
Commercial mortgage-backed securities
Fair Value
Less Than Twelve Months	157.0
Twelve Months or More	75.0
Total	232.0
Gross   Unrealized  Losses
Less Than Twelve Months	5.0
Twelve Months or More	3.0
Total	8.0
Residential mortgage-backed securities
Fair Value
Less Than Twelve Months	6.0
Twelve Months or More	0.0
Total	6.0
Gross   Unrealized  Losses
Less Than Twelve Months	0.0
Twelve Months or More	0.0
Total	0.0
Fixed Maturities
Gross   Unrealized  Losses
Twelve Months or More	$ 11.2