Segment Information - Schedule of consolidated non-current assets by geographic area (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	$ 588	$ 564
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	288	239
Americas other than U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	44	47
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	58	68
Europe, Middle East, & Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	101	114
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	$ 97	$ 96