Fair Value Measurements - Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance for Residential Mortgage Loans Measured at Fair Value (Details) - Residential mortgage loans - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Aggregate Fair Value
Residential mortgage loans measured at fair value	$ 626	$ 450
Past due loans of 30-89 days	1	1
Nonaccrual loans	1	2
Aggregate Unpaid Principal Balance
Residential mortgage loans measured at fair value	624	456
Past due loans of 30-89 days	1	1
Nonaccrual loans	1	2
Difference
Residential mortgage loans measured at fair value	2	(6)
Past due loans of 30-89 days	0	0
Nonaccrual loans	$ 0	$ 0