Accumulated Other Comprehensive Loss - AOCI Activity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 10,437
Other comprehensive income (loss) before reclassifications	18	$ 67
Amounts reclassified from accumulated other comprehensive loss	12	44
Other comprehensive income	30	111
Balance at end of period	10,995	12,282
Defined Benefit Plan | Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(985)	(1,577)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	17	26
Other comprehensive income	17	26
Balance at end of period	(968)	(1,551)
Defined Benefit Plan | Post-Retirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	308	(164)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	(5)	1
Other comprehensive income	(5)	1
Balance at end of period	303	(163)
Foreign Currency Translation Adjustment and Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(422)	(400)
Other comprehensive income (loss) before reclassifications	18	67
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive income	18	67
Balance at end of period	(404)	(333)
Interest Rate Swap
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(17)
Other comprehensive income (loss) before reclassifications		0
Amounts reclassified from accumulated other comprehensive loss		17
Other comprehensive income		17
Balance at end of period		0
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(1,099)	(2,158)
Other comprehensive income	30	111
Balance at end of period	$ (1,069)	$ (2,047)