Segment Information - Schedule of consolidated non-current assets by geographic area (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	$ 564	$ 550
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	239	243
Americas other than U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	47	60
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	68	65
Europe, Middle East, & Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	114	85
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Noncurrent assets	$ 96	$ 97