Fair Value Measurement - Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Carrying amount and estimated fair value financial instruments
Assets of CIVs	$ 378	$ 366
Other Assets	698	706
Long-term debt	(1,696)	(1,694)
Other liabilities	(410)	(439)
Carrying Amount
Carrying amount and estimated fair value financial instruments
Assets of CIVs	25	19
Other Assets	75	79
Financial guaranty insurance contracts	(2,172)	(2,244)
Long-term debt	(1,696)	(1,694)
Other liabilities	(32)	(15)
Estimated Fair Value
Carrying amount and estimated fair value financial instruments
Assets of CIVs	25	19
Other Assets	75	80
Financial guaranty insurance contracts	(1,860)	(1,811)
Long-term debt	(1,569)	(1,593)
Other liabilities	$ (32)	$ (15)