Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income available to IPG common stockholders	$ 146.2	$ 128.6	$ 262.4	$ 290.9
Weighted-average number of common shares outstanding, Basic	389.5	397.7	391.2	399.5
Restricted stock, stock options and other equity awards	7.7	10.2	7.4	9.3
Weighted-average number of common shares outstanding, Diluted	397.2	407.9	398.6	408.8
Earnings per share, Basic	$ 0.38	$ 0.32	$ 0.67	$ 0.73
Earnings per share, Diluted	$ 0.37	$ 0.32	$ 0.66	$ 0.71