Accumulated Other Comprehensive Loss - AOCI Activity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			$ 417
Other comprehensive income (loss) before reclassifications				$ 3
Amounts reclassified from accumulated other comprehensive loss			44	39
Other comprehensive income (loss)	$ 20	$ (4)	44	42
Balance at end of period	342	2,156	342	2,156
Defined Benefit Plan | Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(1,045)	(985)
Other comprehensive income (loss) before reclassifications				0
Amounts reclassified from accumulated other comprehensive loss			57	55
Other comprehensive income (loss)			57	55
Balance at end of period	(988)	(930)	(988)	(930)
Defined Benefit Plan | Post-Retirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			276	308
Other comprehensive income (loss) before reclassifications				0
Amounts reclassified from accumulated other comprehensive loss			(13)	(16)
Other comprehensive income (loss)			(13)	(16)
Balance at end of period	263	292	263	292
Foreign Currency Translation Adjustment and Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(41)	(422)
Other comprehensive income (loss) before reclassifications				3
Amounts reclassified from accumulated other comprehensive loss			0	0
Other comprehensive income (loss)			0	3
Balance at end of period	(41)	(419)	(41)	(419)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(786)	(1,053)	(810)	(1,099)
Other comprehensive income (loss)	20	(4)	44	42
Balance at end of period	$ (766)	$ (1,057)	$ (766)	$ (1,057)