Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income available to IPG common stockholders	$ 165.6	$ 161.0	$ 327.1	$ 292.7
Weighted-average number of common shares outstanding, Basic	386.7	382.6	385.8	383.2
Dilutive effect of stock options and restricted shares	5.1	5.8	4.5	5.2
Weighted-average number of common shares outstanding, Diluted	391.8	388.4	390.3	388.4
Loss per share, Basic	$ 0.43	$ 0.42	$ 0.85	$ 0.76
Loss per share, Diluted	$ 0.42	$ 0.41	$ 0.84	$ 0.75