Deferred Revenue - Schedule of Rollforward (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Roll Forward]
Beginning balance	$ 201	$ 217
Additions	819	728
Amortization	(660)	(613)
Ending balance	360	332
Annual Listings Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	0	0
Additions	384	387
Amortization	(288)	(289)
Ending balance	96	98
Original Listings Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	19	25
Additions	9	11
Amortization	(15)	(17)
Ending balance	13	19
Other Listings Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	94	100
Additions	34	30
Amortization	(31)	(30)
Ending balance	97	100
Data Services and Other Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	88	92
Additions	367	300
Amortization	(326)	(277)
Ending balance	129	$ 115
Mortgage Technology
Disaggregation Of Revenue [Roll Forward]
Beginning balance	0
Additions	25
Amortization	0
Ending balance	$ 25