Deferred Revenue - Schedule of Changes in Deferred Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disaggregation Of Revenue [Roll Forward]
Deferred revenue, beginning balance	$ 216	$ 198
Additions	812	818
Amortization	(811)	(801)
Acquisitions, net of divestitures (Note 3)		1
Deferred revenue, ending balance	217	216
Annual Listing Revenue
Disaggregation Of Revenue [Roll Forward]
Deferred revenue, beginning balance	0	0
Additions	384	368
Amortization	(384)	(368)
Acquisitions, net of divestitures (Note 3)		0
Deferred revenue, ending balance	0	0
Original Listing Revenues
Disaggregation Of Revenue [Roll Forward]
Deferred revenue, beginning balance	25	23
Additions	24	22
Amortization	(24)	(20)
Acquisitions, net of divestitures (Note 3)		0
Deferred revenue, ending balance	25	25
Other Listing Revenues
Disaggregation Of Revenue [Roll Forward]
Deferred revenue, beginning balance	98	83
Additions	38	54
Amortization	(36)	(39)
Acquisitions, net of divestitures (Note 3)		0
Deferred revenue, ending balance	100	98
Data Services and Other Revenues
Disaggregation Of Revenue [Roll Forward]
Deferred revenue, beginning balance	93	92
Additions	366	374
Amortization	(367)	(374)
Acquisitions, net of divestitures (Note 3)		1
Deferred revenue, ending balance	$ 92	$ 93