Investments - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2024 USD ($) investment	Dec. 31, 2023 USD ($) investment
Investment [Line Items]
Percentage of securities representing gross unrealized losses	11.00%	11.00%
Percentage of gross unrealized losses in a continuous loss position less than twelve months	6.00%	8.00%
Individual securities comprising total gross unrealized losses | investment	2,282	3,096
Approximate percentage, outstanding principal balance of commercial mortgage loans	35.00%
Minimum
Investment [Line Items]
Outstanding balance of commercial mortgage loans (less than)	$ 0.1	$ 0.1
Maximum
Investment [Line Items]
Outstanding balance of commercial mortgage loans (less than)	$ 5.0	$ 10.0