Segment and Related Information - Operating Results by Segment (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) Segment	Mar. 31, 2017 USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| Segment	4
Segment Reporting Information [Line Items]
Revenue	$ 1,567	$ 1,453
Operating Profit	711	639
Amortization of intangibles	24	24
Ratings
Segment Reporting Information [Line Items]
Legal settlement		2
Amortization of intangibles		1
Market Intelligence
Segment Reporting Information [Line Items]
Amortization of intangibles		17
Non-cash acquisition and disposition-related adjustments		4
Platts
Segment Reporting Information [Line Items]
Amortization of intangibles	5	5
Non-cash acquisition and disposition-related adjustments		11
Indices
Segment Reporting Information [Line Items]
Amortization of intangibles	2	1
Operating Segments
Segment Reporting Information [Line Items]
Revenue	1,567	1,453
Operating Profit	757	675
Operating Segments \| Ratings
Segment Reporting Information [Line Items]
Revenue	748	714
Operating Profit	408	374
Operating Segments \| Market Intelligence
Segment Reporting Information [Line Items]
Revenue	437	402
Operating Profit	112	104
Operating Segments \| Platts
Segment Reporting Information [Line Items]
Revenue	196	191
Operating Profit	90	82
Operating Segments \| Indices
Segment Reporting Information [Line Items]
Revenue	214	171
Operating Profit	147	115
Intersegment Elimination
Segment Reporting Information [Line Items]
Revenue	(28)	(25)
Operating Profit	0	0
Unallocated expense
Segment Reporting Information [Line Items]
Revenue	0	0
Operating Profit	$ (46)	$ (36)

Non-Cash Acquisition and Disposition Expense

No definition available.

Name:	spgi_NonCashAcquisitionandDispositionExpense
Namespace Prefix:	spgi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

+ Details

Name:	us-gaap_AmortizationOfIntangibleAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of litigation expense, including but not limited to legal, forensic, accounting, and investigative fees.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_SegmentReportingAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=spgi_RatingsSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=spgi_MarketIntelligenceSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=spgi_PlattsSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=spgi_IndicesSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_IntersegmentEliminationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_MaterialReconcilingItemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: