Accumulated Other Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	$ 377	$ 409	$ 1,150	$ 1,272
Other (expense) income, net	(38)	1	48	(73)
Total before tax	716	480	2,022	1,426
Income tax expense	(172)	(114)	(497)	(369)
Net of tax	544	366	1,525	1,057
Decrease (Increase) in Net Income | Interest rate swaps
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	21	20	62	41
Income tax expense	(5)	(5)	(15)	(10)
Net of tax	16	15	47	31
Decrease (Increase) in Net Income | Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Other (expense) income, net	108	50	208	152
Decrease (Increase) in Net Income | Prior service cost
Reclassifications out of accumulated other comprehensive income loss by component
Other (expense) income, net	1	1	4	5
Decrease (Increase) in Net Income | Curtailment loss
Reclassifications out of accumulated other comprehensive income loss by component
Other (expense) income, net		4		4
Decrease (Increase) in Net Income | Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	109	55	212	161
Income tax expense	(27)	(13)	(52)	(39)
Net of tax	$ 82	$ 42	$ 160	$ 122