Earnings per Share - Summary (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amount attributable to S&P Global Inc. common shareholders:
Net income	$ 454	$ 455	$ 792	$ 639	$ 541	$ 617	$ 555	$ 410	$ 2,339	$ 2,123	$ 1,958
Basic weighted-average number of common shares outstanding (shares)									241,000,000.0	245,400,000	250,900,000
Effect of stock options and other dilutive securities (shares)									1,100,000	1,500,000	2,300,000
Diluted weighted-average number of common shares outstanding (shares)									242,100,000	246,900,000	253,200,000
Net income:
Basic (USD per share)	$ 1.89	$ 1.89	$ 3.29	$ 2.64	$ 2.22	$ 2.52	$ 2.25	$ 1.66	$ 9.71	$ 8.65	$ 7.80
Diluted (USD per share)	$ 1.88	$ 1.88	$ 3.28	$ 2.62	$ 2.20	$ 2.50	$ 2.24	$ 1.65	$ 9.66	$ 8.60	$ 7.73
Employee Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares not included in the computation of diluted earnings per share for both restricted stock and stock options (shares)									0	0	0
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares not included in the computation of diluted earnings per share for both restricted stock and stock options (shares)									400,000	400,000	500,000