Revenue Recognition - Reconciliation of Total Revenue (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	$ 1,801	$ 2,011	$ 5,518	$ 6,069
Adjustments for non-ASC 606 revenue	(118)	(123)	(360)	(375)
Total revenue from contracts with customers	$ 1,683	$ 1,888	$ 5,158	$ 5,694