Accumulated Other Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	$ 389	$ 449
Other income (expense), net	34	(98)
Total before tax	632	433
Income tax expense	(157)	(119)
Net of tax	475	314
Decrease (Increase) in Net Income | Interest rate swaps
Reclassifications out of accumulated other comprehensive income loss by component
Interest expense	20	5
Income tax expense	(5)	0
Net of tax	15	5
Decrease (Increase) in Net Income | Net actuarial loss
Reclassifications out of accumulated other comprehensive income loss by component
Other income (expense), net	50	50
Decrease (Increase) in Net Income | Prior service cost
Reclassifications out of accumulated other comprehensive income loss by component
Other income (expense), net	2	1
Decrease (Increase) in Net Income | Defined benefit plan
Reclassifications out of accumulated other comprehensive income loss by component
Total before tax	52	51
Income tax expense	(13)	(12)
Net of tax	$ 39	$ 39