Reinsurance - Schedule of Credit Ratings on Reinsurance Recoverable (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	$ 16,919.0	$ 16,925.0
Reinsurance recoverable allowance for credit loss	23.0	24.0	$ 29.0	$ 63.0
A++
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	720.0	686.0
A+
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	3,274.0	3,095.0
A
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	321.0	358.0
Non rated
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	12,604.0	12,786.0
Reinsurance recoverable allowance for credit loss	0.0	0.0
Collateralized
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	14,137.0	14,249.0
Collateralized | A++
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	0.0	0.0
Collateralized | A+
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	1,510.0	1,441.0
Collateralized | A
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	33.0	33.0
Collateralized | Non rated
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	12,594.0	12,775.0
Non-collateralized
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	2,782.0	2,676.0
Non-collateralized | A++
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	720.0	686.0
Non-collateralized | A+
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	1,764.0	1,654.0
Non-collateralized | A
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	288.0	325.0
Non-collateralized | Non rated
Ceded Credit Risk [Line Items]
Total reinsurance recoverable	$ 10.0	$ 11.0