Segment and Geographical Information - Net Revenues and Long-Lived Assets by Geographical Areas (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	$ 2,297	$ 1,983	$ 4,434	$ 3,857
Long-lived assets	4,855		4,855		$ 4,185
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	1,170	982	2,200	1,885
Long-lived assets	4,393		4,393		3,784
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	286	283	563	553
Rest of world
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	841	$ 718	1,671	$ 1,419
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 462		$ 462		$ 401