Accumulated Other Comprehensive Loss - Changes in AOCL, After Tax and Minority Interest (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 3,259	$ 4,545
Ending balance	4,506	3,039
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	(72)	(237)
Amounts reclassified from accumulated other comprehensive loss	0	0
Ending balance	(1,356)	(1,393)
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	1
Amounts reclassified from accumulated other comprehensive loss	0
Ending balance	1
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	22	(12)
Amounts reclassified from accumulated other comprehensive loss	102	96
Ending balance	(2,732)	(2,899)
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	2	18
Amounts reclassified from accumulated other comprehensive loss	(2)	(11)
Ending balance	5	10
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	(47)	(231)
Amounts reclassified from accumulated other comprehensive loss	100	85
Ending balance	$ (4,082)	$ (4,282)