Accumulated Other Comprehensive Loss - Changes in AOCL, After Tax and Minority Interest (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 3,259	$ 4,545
Ending balance	4,411	3,013
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	(2)	(223)
Amounts reclassified from accumulated other comprehensive loss	0	0
Ending balance	(1,282)	(1,379)
Unrealized Gains (Losses) from Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0
Other comprehensive income (loss) before reclassifications	8
Ending balance	8
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	16	(9)
Amounts reclassified from accumulated other comprehensive loss	68	55
Ending balance	(2,772)	(2,937)
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	0	19
Amounts reclassified from accumulated other comprehensive loss	(2)	(8)
Ending balance	3	14
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	26	(213)
Amounts reclassified from accumulated other comprehensive loss	66	47
Ending balance	$ (4,043)	$ (4,302)