Accumulated Other Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	$ 384	$ 414	$ 773	$ 863
Other income (expense), net	52	24	86	(74)
Total before tax	674	513	1,306	946
Income tax expense	(168)	(136)	(325)	(255)
Net of tax	506	377	981	691
Decrease (Increase) in Net Income | Interest rate swaps
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	21	16	41	21
Income tax expense	(5)	(5)	(10)	(5)
Net of tax	16	11	31	16
Decrease (Increase) in Net Income | Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Other income (expense), net	50	52	100	102
Decrease (Increase) in Net Income | Prior service cost
Reclassifications out of accumulated other comprehensive income loss by component
Other income (expense), net	1	3	3	4
Decrease (Increase) in Net Income | Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	51	55	103	106
Income tax expense	(12)	(14)	(25)	(26)
Net of tax	$ 39	$ 41	$ 78	$ 80