Deferred Revenue - Schedule of Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Roll Forward]
Beginning balance	$ 217	$ 216
Additions	544	549
Amortization	(196)	(205)
Ending balance	565	560
Annual Listings Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	0	0
Additions	382	380
Amortization	(96)	(95)
Ending balance	286	285
Original Listings Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	25	25
Additions	3	7
Amortization	(6)	(6)
Ending balance	22	26
Other Listings Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	100	98
Additions	20	15
Amortization	(9)	(8)
Ending balance	111	105
Data Services and Other Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	92	93
Additions	139	147
Amortization	(85)	(96)
Ending balance	$ 146	$ 144