Employee Benefits - Change in Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Combined Pension Plan
Change in benefit obligation
Benefit obligation at beginning of year	$ 5,295	$ 9,678	$ 12,202
Plan spin-off/ Benefit obligation transferred upon sale of business	0	(2,552)	0
Service cost	25	37	56
Interest cost	270	154	201
Plan amendments	0	0	(13)
Special termination benefits charge	2	0	6
Actuarial loss (gain)	114	(1,432)	(337)
Benefits paid from plan assets	(494)	(590)	(766)
Settlement payments and annuity purchase	0	0	(1,671)
Benefit obligation at end of year	5,212	5,295	9,678
Post-Retirement Benefit Plans
Change in benefit obligation
Benefit obligation at beginning of year	1,995	2,781	3,048
Plan spin-off/ Benefit obligation transferred upon sale of business	0	(26)	0
Service cost	5	10	14
Interest cost	103	72	47
Participant contributions	32	37	41
Direct subsidy receipts	2	2	3
Plan amendments	0	(41)	0
Actuarial loss (gain)	14	(591)	(125)
Benefits paid by company	(228)	(249)	(247)
Benefits paid from plan assets	(4)	0	0
Benefit obligation at end of year	$ 1,919	$ 1,995	$ 2,781