Accumulated Other Comprehensive Loss - AOCI Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 11,840	$ 11,162
Other comprehensive income (loss) before reclassifications	437	155
Amounts reclassified from accumulated other comprehensive loss	622	500
Net Change in AOCL	1,059	655	$ (133)
Balance at end of period	10,437	11,840	11,162
Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(1,741)	(2,469)
Other comprehensive income (loss) before reclassifications	571	291
Amounts reclassified from accumulated other comprehensive loss	493	437
Net Change in AOCL	1,064	728
Balance at end of period	(677)	(1,741)	(2,469)
Defined Benefit Plans | Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(1,577)	(2,197)
Other comprehensive income (loss) before reclassifications	98	197
Amounts reclassified from accumulated other comprehensive loss	494	423
Net Change in AOCL	592	620
Balance at end of period	(985)	(1,577)	(2,197)
Defined Benefit Plans | Post-Retirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(164)	(272)
Other comprehensive income (loss) before reclassifications	473	94
Amounts reclassified from accumulated other comprehensive loss	(1)	14
Net Change in AOCL	472	108
Balance at end of period	308	(164)	(272)
Foreign Currency Translation Adjustment and Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(400)	(265)
Other comprehensive income (loss) before reclassifications	(134)	(135)
Amounts reclassified from accumulated other comprehensive loss	112	0
Net Change in AOCL	(22)	(135)
Balance at end of period	(422)	(400)	(265)
Interest Rate Swap
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(17)	(79)
Other comprehensive income (loss) before reclassifications	0	(1)
Amounts reclassified from accumulated other comprehensive loss	17	63
Net Change in AOCL	17	62
Balance at end of period	0	(17)	(79)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(2,158)	(2,813)	(2,680)
Net Change in AOCL	1,059	655	(133)
Balance at end of period	$ (1,099)	$ (2,158)	$ (2,813)