Stock-Based Compensation - Common Shares Reserved for Issuance (Details) - shares shares in Millions	Dec. 31, 2019	Dec. 31, 2018
Number of common shares reserved for issuance
Shares available for granting under the 2019 plan (in shares)	20.0	33.3
Options outstanding (shares)	0.7	1.7
Total shares reserved for issuance (in shares)	20.7	35.0
Director Deferred Stock Ownership Plan
Number of common shares reserved for issuance
Total shares reserved for issuance (in shares)		1.0

Share based compensation arrangement by share based payment award, total number of shares reserved for issuance.

No definition available.

Name:	spgi_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesReservedForIssuance
Namespace Prefix:	spgi_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Share based compensation arrangement by share based payment award number of shares reserved for issuance.

+ References

No definition available.

+ Details

Name:	spgi_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesReservedForIssuanceAbstract
Namespace Prefix:	spgi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_PlanNameAxis=spgi_DirectorDeferredStockOwnershipPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: