Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income available to IPG common stockholders	$ 169.5	$ 145.8	$ 161.5	$ 131.7
Weighted-average number of common shares outstanding, Basic	386.2	383.6	385.4	383.5
Dilutive effect of stock options and restricted shares	5.0	5.9	4.7	5.4
Weighted-average number of common shares outstanding, Diluted	391.2	389.5	390.1	388.9
Loss per share, Basic	$ 0.44	$ 0.38	$ 0.42	$ 0.34
Loss per share, Diluted	$ 0.43	$ 0.37	$ 0.41	$ 0.34