Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Earnings Per Share [Abstract]
Net income available to IPG common stockholders	$ 162.5	$ 214.5	$ 77.1	$ 324.9
Weighted-average number of common shares outstanding - basic (in shares)	367.9	376.3	370.2	377.4
Dilutive effect of stock options and restricted shares (in shares)	2.2	2.4	2.3	2.3
Weighted-average number of common shares outstanding - diluted (in shares)	370.1	378.7	372.5	379.7
Earnings per share available to IPG common stockholders:
Basic (in dollars per share)	$ 0.44	$ 0.57	$ 0.21	$ 0.86
Diluted (in dollars per share)	$ 0.44	$ 0.57	$ 0.21	$ 0.86