Geographical Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	$ 3,136	$ 2,650	$ 6,111	$ 5,194
Long-lived assets	1,479		1,479		$ 1,482
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	1,690	1,407	3,296	2,750
Long-lived assets	1,393		1,393		1,391
U.K.
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	334	318	647	625
Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	1,112	$ 925	2,168	$ 1,819
Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 86		$ 86		$ 91