Fair Value Measurement - Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Carrying amount and estimated fair value financial instruments
Assets of CIVs	$ 359	$ 366
Other assets (including other invested assets)	686	706
Long-term debt	(1,698)	(1,694)
Other liabilities	(496)	(439)
Carrying Amount
Carrying amount and estimated fair value financial instruments
Assets of CIVs	31	19
Other assets (including other invested assets)	115	79
Financial guaranty insurance contracts	(1,946)	(2,244)
Long-term debt	(1,698)	(1,694)
Other liabilities	(71)	(15)
Estimated Fair Value
Carrying amount and estimated fair value financial instruments
Assets of CIVs	31	19
Other assets (including other invested assets)	116	80
Financial guaranty insurance contracts	(1,709)	(1,811)
Long-term debt	(1,625)	(1,593)
Other liabilities	$ (71)	$ (15)