Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income available to IPG common stockholders	$ 279.7	$ 165.6	$ 238.8	$ 327.1
Weighted-average number of common shares outstanding, Basic	389.6	386.7	388.9	385.8
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	4.3	5.1	3.7	4.5
Weighted-average number of common shares outstanding, Diluted	393.9	391.8	392.6	390.3
Earnings per share, Basic	$ 0.72	$ 0.43	$ 0.61	$ 0.85
Earnings per share, Diluted	$ 0.71	$ 0.42	$ 0.61	$ 0.84