Investments - Amortization by Expected Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Amortized cost of fixed maturities available-for-sale
Due in one year or less	$ 2,021.5
Due after one year through five years	9,355.6
Due after five years through ten years	12,967.0
Due after ten years	28,086.3
Subtotal	52,430.4
Mortgage-backed and other asset-backed securities	18,482.0
Amortized cost, fixed maturities	70,912.4	$ 72,869.9
Fair value of fixed maturities available-for-sale
Due in one year or less	2,005.8
Due after one year through five years	8,905.8
Due after five years through ten years	11,592.6
Due after ten years	23,143.6
Subtotal	45,647.8
Mortgage-backed and other asset-backed securities	16,761.3
Fair value, fixed maturities	$ 62,409.1	$ 78,154.5