Earnings Per Share - Summary (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Amounts attributable to S&P Global Inc. common shareholders:
Net income	$ 495	$ 414	$ 1,447	$ 1,234
Basic weighted-average number of common shares outstanding	251.3	255.5	251.6	257.0
Effect of stock options and other dilutive securities	2.2	2.4	2.1	2.5
Diluted weighted-average number of common shares outstanding	253.5	257.9	253.7	259.5
Earnings per share attributable to S&P Global Inc. common shareholders:
Basic (USD per share)	$ 1.97	$ 1.62	$ 5.75	$ 4.80
Diluted (USD per share)	$ 1.95	$ 1.61	$ 5.70	$ 4.75