Business Segments - Revenue and Long-Lived Assets by Geographic Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Geographic Segments
Total revenue	$ 2,724	$ 3,400	$ 3,363
Property and equipment, net	415	500
U.S.
Geographic Segments
Total revenue	1,819	2,195	2,190
Property and equipment, net	260	299
Other
Geographic Segments
Total revenue	905	1,205	$ 1,173
Property and equipment, net	$ 155	$ 201