Segment and Geographic Information - Summary of Revenue by Geographic Area (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenue	$ 288	$ 354	$ 323	$ 281	$ 213	$ 255	$ 247	$ 230	$ 1,246	$ 945	$ 763
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenue									593	463	386
United Kingdom
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenue									191	141	110
All Other Countries
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenue									$ 462	$ 341	$ 267