Accumulated Other Comprehensive Loss - Changes in AOCL, After Tax and Minority Interest (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 3,259	$ 4,545
Ending balance	3,286	3,697
Foreign Currency Translation Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,284)	(1,156)
Other comprehensive income (loss) before reclassifications	(32)	(216)
Amounts reclassified from accumulated other comprehensive loss	0	0
Ending balance	(1,316)	(1,372)
Unrecognized Net Actuarial Losses and Prior Service Costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(2,856)	(2,983)
Other comprehensive income (loss) before reclassifications	9	(1)
Amounts reclassified from accumulated other comprehensive loss	27	26
Ending balance	(2,820)	(2,958)
Deferred Derivative Gains (Losses)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	5	3
Other comprehensive income (loss) before reclassifications	1	18
Amounts reclassified from accumulated other comprehensive loss	(2)	(4)
Ending balance	4	17
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4,135)	(4,136)
Other comprehensive income (loss) before reclassifications	(22)	(199)
Amounts reclassified from accumulated other comprehensive loss	25	22
Ending balance	$ (4,132)	$ (4,313)