Accumulated Other Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	$ 414	$ 518	$ 863	$ 1,041
Other income, net	24	44	(74)	39
Total before tax	513	502	946	(5,525)
Income tax expense	(136)	(131)	(255)	(269)
Net of tax	377	371	691	(5,794)
Decrease (Increase) in Net Income | Interest rate swaps
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	16		21
Income tax expense	(5)		(5)
Net of tax	11		16
Decrease (Increase) in Net Income | Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Other income, net	52	56	102	113
Decrease (Increase) in Net Income | Prior service cost
Reclassifications out of accumulated other comprehensive income loss by component
Other income, net	3	2	4	4
Decrease (Increase) in Net Income | Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	55	58	106	117
Income tax expense	(14)	(14)	(26)	(29)
Net of tax	$ 41	$ 44	$ 80	$ 88