Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income available to IPG common stockholders	$ 145.8	$ 107.7	$ 131.7	$ 132.4
Weighted-average number of common shares outstanding, Basic	383.6	392.3	383.5	392.0
Dilutive effect of stock options and restricted shares	5.9	8.0	5.4	7.6
Weighted-average number of common shares outstanding, Diluted	389.5	400.3	388.9	399.6
Earnings per share, Basic	$ 0.38	$ 0.27	$ 0.34	$ 0.34
Earnings per share, Diluted	$ 0.37	$ 0.27	$ 0.34	$ 0.33