Deferred Revenue - Schedule of Changes in Deferred Revenue (Details) - USD ($) $ in Millions			3 Months Ended
	Jan. 01, 2018	Jan. 01, 2017	Mar. 31, 2018	Mar. 31, 2017
Movement in Deferred Revenue [Roll Forward]
Deferred revenue balance at December 31, 2017	$ 216	$ 194	$ 216	$ 194
Additions			549	535
Amortization	(49)	(45)	(205)	(208)
Deferred revenue balance at March 31, 2018			560	521
Annual Listings Revenue
Movement in Deferred Revenue [Roll Forward]
Deferred revenue balance at December 31, 2017	0	0	0	0
Additions			380	361
Amortization			(95)	(91)
Deferred revenue balance at March 31, 2018			285	270
Original Listings Revenues
Movement in Deferred Revenue [Roll Forward]
Deferred revenue balance at December 31, 2017	25	23	25	23
Additions			7	2
Amortization			(6)	(5)
Deferred revenue balance at March 31, 2018			26	20
Other Listings Revenues
Movement in Deferred Revenue [Roll Forward]
Deferred revenue balance at December 31, 2017	98	83	98	83
Additions			15	24
Amortization			(8)	(12)
Deferred revenue balance at March 31, 2018			105	95
Data Services and Other Revenues
Movement in Deferred Revenue [Roll Forward]
Deferred revenue balance at December 31, 2017	$ 93	$ 88	93	88
Additions			147	148
Amortization			(96)	(100)
Deferred revenue balance at March 31, 2018			$ 144	$ 136