Deferred Revenue - Schedule of Rollforward (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Disaggregation Of Revenue [Roll Forward]
Beginning balance	$ 259	$ 201
Additions	739	698
Amortization	(460)	(434)
Ending balance	538	465
Annual Listings Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	0	0
Additions	384	383
Amortization	(197)	(191)
Ending balance	187	192
Original Listings Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	13	19
Additions	19	6
Amortization	(14)	(9)
Ending balance	18	16
Other Listings Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	92	94
Additions	34	25
Amortization	(22)	(22)
Ending balance	104	97
Data Services and Other Revenues
Disaggregation Of Revenue [Roll Forward]
Beginning balance	95	88
Additions	265	284
Amortization	(206)	(212)
Ending balance	154	$ 160
Mortgage Technology
Disaggregation Of Revenue [Roll Forward]
Beginning balance	59
Additions	37
Amortization	(21)
Ending balance	$ 75