Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Amounts attributable to S&P Global Inc. common shareholders:
Net income	$ 491	$ 399
Basic weighted-average number of common shares outstanding	252,400,000	258,200,000
Effect of stock options and other dilutive securities (shares)	2,000,000	2,600,000
Diluted weighted-average number of common shares outstanding	254,400,000	260,800,000
Earnings per share attributable to S&P Global Inc. common shareholders:
Basic (USD per share)	$ 1.94	$ 1.54
Diluted (USD per share)	$ 1.93	$ 1.53
Employee stock option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding stock not included in the computation of diluted earnings per share (shares)	0	0
Restricted performance shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding stock not included in the computation of diluted earnings per share (shares)	600,000	700,000