Accumulated Other Comprehensive Loss - AOCI Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 11,162	$ 13,470
Other comprehensive income (loss) before reclassifications	155	(341)
Amounts reclassified from accumulated other comprehensive loss	500	208
Net Change in AOCL	655	(133)	$ (219)
Balance at end of period	11,840	11,162	13,470
Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(2,469)	(2,413)
Other comprehensive income (loss) before reclassifications	291	(218)
Amounts reclassified from accumulated other comprehensive loss	437	162
Net Change in AOCL	728	(56)
Balance at end of period	(1,741)	(2,469)	(2,413)
Defined Benefit Plans | Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(2,197)	(2,229)
Other comprehensive income (loss) before reclassifications	197	(115)
Amounts reclassified from accumulated other comprehensive loss	423	147
Net Change in AOCL	620	32
Balance at end of period	(1,577)	(2,197)	(2,229)
Defined Benefit Plans | Post-Retirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(272)	(184)
Other comprehensive income (loss) before reclassifications	94	(103)
Amounts reclassified from accumulated other comprehensive loss	14	15
Net Change in AOCL	108	(88)
Balance at end of period	(164)	(272)	(184)
Foreign Currency Translation Adjustment and Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(265)	(228)
Other comprehensive income (loss) before reclassifications	(135)	(37)
Amounts reclassified from accumulated other comprehensive loss	0	0
Net Change in AOCL	(135)	(37)
Balance at end of period	(400)	(265)	(228)
Interest Rate Swap
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(79)	(39)
Other comprehensive income (loss) before reclassifications	(1)	(86)
Amounts reclassified from accumulated other comprehensive loss	63	46
Net Change in AOCL	62	(40)
Balance at end of period	(17)	(79)	(39)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(2,813)	(2,680)	(2,461)
Net Change in AOCL	655	(133)	(219)
Balance at end of period	$ (2,158)	$ (2,813)	$ (2,680)