Stockholders' Equity - Components of AOCI (Details) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	May 18, 2023	May 17, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity	$ 2,445	$ 2,572	$ 2,766	$ 2,534	$ 2,358	$ 2,460	$ 2,431	$ 2,431
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity	(5)	$ (29)	$ (27)	$ (23)	(12)	$ (3)	$ 0	$ 0	$ (167)
Available-for-sale securities unrealized gain (loss), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity	7				(12)
Postretirement benefit prior service credits (costs), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity	16				0
Postretirement benefit actuarial gain (loss), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Equity	$ (28)				$ 0