Revenue Recognition - Revenue not Under ASC 606 (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Total revenue	$ 5,167	$ 5,350	$ 15,587	$ 16,152
Adjustments for non-ASC 606 revenue	(481)	(355)	(1,443)	(1,069)
Total revenue from contracts with customers	$ 4,686	$ 4,995	$ 14,144	$ 15,083