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Segment and Geographic Information - Narrative (Details) | 12 Months Ended
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Dec. 31, 2017 Segment
Segment Reporting [Abstract] |
Number of reportable segments | 3
Maximum percentage of consolidated revenue represented by foreign countries (more than) | 7.00%
Maximum percentage of consolidated revenue represented by single customer (more than) | 10.00%

X
- Definition Maximum percentage of consolidated revenue represented by foreign countries. + References No definition available. + Details
Name: | spgi_MaximumPercentageOfConsolidatedRevenueRepresentedByForeignCountries
Namespace Prefix: | spgi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum percentage of consolidated revenue represented by single customer. + References No definition available. + Details
Name: | spgi_MaximumPercentageOfConsolidatedRevenueRepresentedBySingleCustomer
Namespace Prefix: | spgi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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

X
- References No definition available. + Details
Name: | us-gaap_SegmentReportingAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration