Revenue Recognition - Revenue Not Subject to Topic 606 (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Total revenue	$ 2,014	$ 2,052	$ 4,060	$ 4,139
Adjustments for non-ASC 606 revenue	(89)	(80)	(194)	(149)
Total revenue from contracts with customers	$ 1,925	$ 1,972	$ 3,866	$ 3,990