Accumulated Other Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	$ 409	$ 496	$ 1,272	$ 1,537
Other income (loss), net	1	(44)	(73)	(5)
Total before tax	480	410	1,426	(5,115)
Income tax expense	(114)	(108)	(369)	(377)
Net of tax	366	302	1,057	(5,492)
Decrease (Increase) in Net Income | Interest rate swaps
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	20		41
Income tax expense	(5)		(10)
Net of tax	15		31
Decrease (Increase) in Net Income | Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Other income (loss), net	50	54	152	167
Decrease (Increase) in Net Income | Prior service cost
Reclassifications out of accumulated other comprehensive income loss by component
Other income (loss), net	1	3	5	7
Decrease (Increase) in Net Income | Curtailment loss
Reclassifications out of accumulated other comprehensive income loss by component
Other income (loss), net	4		4
Decrease (Increase) in Net Income | Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	55	57	161	174
Income tax expense	(13)	(14)	(39)	(43)
Net of tax	$ 42	$ 43	$ 122	$ 131