Employee Benefits - Change in Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in plan assets
Return on plan assets	$ 255	$ (987)
Combined Pension Plan
Change in plan assets
Fair value of plan assets at beginning of year	4,715	8,531	$ 10,546
Plan spin-off	0	(2,239)	0
Return on plan assets	255	(987)	422
Benefits paid from plan assets	(494)	(590)	(766)
Settlement payments and annuity purchase	0	0	(1,671)
Fair value of plan assets at end of year	$ 4,476	$ 4,715	$ 8,531