Nature of Operations and Basis of Presentation - Revenue Disaggregated by Revenue Type (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	$ 1,609	$ 1,509	$ 3,176	$ 2,962
Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	5	0	5	0
Intersegment Elimination
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	(32)	(28)	(60)	(53)
Ratings | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	775	747	1,523	1,461
Market Intelligence | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	447	414	884	816
Platts | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	205	192	401	383
Indices | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	209	184	423	355
Subscription
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	660	608	1,297	1,197
Subscription | Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	5	0	5	0
Subscription | Intersegment Elimination
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Subscription | Ratings | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Subscription | Market Intelligence | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	431	397	854	783
Subscription | Platts | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	188	174	369	346
Subscription | Indices | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	36	37	69	68
Non-transaction
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	346	325	697	641
Non-transaction | Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Non-transaction | Intersegment Elimination
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	(32)	(28)	(60)	(53)
Non-transaction | Ratings | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	378	353	757	694
Non-transaction | Market Intelligence | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Non-transaction | Platts | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Non-transaction | Indices | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Non-subscription / Transaction
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	412	409	792	796
Non-subscription / Transaction | Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Non-subscription / Transaction | Intersegment Elimination
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Non-subscription / Transaction | Ratings | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	397	394	766	767
Non-subscription / Transaction | Market Intelligence | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	11	11	20	22
Non-subscription / Transaction | Platts | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	4	4	6	7
Non-subscription / Transaction | Indices | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Asset-linked fees
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	140	120	275	233
Asset-linked fees | Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Asset-linked fees | Intersegment Elimination
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Asset-linked fees | Ratings | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Asset-linked fees | Market Intelligence | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	5	6	10	11
Asset-linked fees | Platts | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Asset-linked fees | Indices | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	135	114	265	222
Sales usage-based royalties
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	51	47	115	95
Sales usage-based royalties | Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Sales usage-based royalties | Intersegment Elimination
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Sales usage-based royalties | Ratings | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Sales usage-based royalties | Market Intelligence | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Sales usage-based royalties | Platts | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	13	14	26	30
Sales usage-based royalties | Indices | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	38	33	89	65
Transferred at Point in Time
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	412	409	792	796
Transferred at Point in Time | Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Transferred at Point in Time | Intersegment Elimination
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Transferred at Point in Time | Ratings | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	397	394	766	767
Transferred at Point in Time | Market Intelligence | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	11	11	20	22
Transferred at Point in Time | Platts | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	4	4	6	7
Transferred at Point in Time | Indices | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	0	0	0	0
Transferred over Time
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	1,197	1,100	2,384	2,166
Transferred over Time | Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	5	0	5	0
Transferred over Time | Intersegment Elimination
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	(32)	(28)	(60)	(53)
Transferred over Time | Ratings | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	378	353	757	694
Transferred over Time | Market Intelligence | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	436	403	864	794
Transferred over Time | Platts | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	201	188	395	376
Transferred over Time | Indices | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer, excluding assessed tax	$ 209	$ 184	$ 423	$ 355