Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Amounts attributable to S&P Global Inc. common shareholders:
Net income	$ 414	$ 892	$ 1,234	$ 1,569
Basic weighted-average number of common shares outstanding	255,500,000	262,900,000	257,000,000	264,100,000
Effect of stock options and other dilutive securities (in shares)	2,400,000	2,400,000	2,500,000	2,300,000
Diluted weighted-average number of common shares outstanding	257,900,000	265,300,000	259,500,000	266,400,000
Earnings per share attributable to S&P Global Inc. common shareholders:
Basic (in dollars per share)	$ 1.62	$ 3.39	$ 4.80	$ 5.94
Diluted (in dollars per share)	$ 1.61	$ 3.36	$ 4.75	$ 5.89
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	0	0	0	0
Restricted performance shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares not included in the computation of diluted earnings per share			900,000	700,000