Revenue Recognition - Revenue not Under ASC 606 (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue from Contract with Customer [Abstract]
Total revenue	$ 1,799	$ 2,028	$ 3,717	$ 4,058
Adjustments for non-ASC 606 revenue	(121)	(125)	(242)	(252)
Total revenue from contracts with customers	$ 1,678	$ 1,903	$ 3,475	$ 3,806