Goodwill and Other Intangible Assets - Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 2,949	$ 2,882
Acquisitions		113
Dispositions		(35)
Other	40	(11)
Goodwill, ending balance	2,989	2,949
Ratings
Goodwill [Roll Forward]
Goodwill, beginning balance	109	114
Acquisitions		0
Dispositions		0
Other	5	(5)
Goodwill, ending balance	114	109
Market and Commodities Intelligence
Goodwill [Roll Forward]
Goodwill, beginning balance	2,457	2,392
Acquisitions		106
Dispositions		(35)
Other	27	(6)
Goodwill, ending balance	2,484	2,457
Indices
Goodwill [Roll Forward]
Goodwill, beginning balance	383	376
Acquisitions		7
Dispositions		0
Other	8	0
Goodwill, ending balance	$ 391	$ 383