Federal Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of beginning-of-year	$ 59	$ 64
Decreases for prior year tax positions	(6)	(6)
Increases for prior year tax positions	23	1
Balance as of end-of-year	$ 76	$ 59