Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Earnings Per Share [Abstract]
Net income available to IPG common stockholders	$ 124.2	$ 20.1	$ 201.3	$ 345.0
Weighted-average number of common shares outstanding - basic (in shares)	365.0	373.9	368.4	376.2
Dilutive effect of stock options and restricted shares (in shares)	3.0	2.9	2.5	2.5
Weighted-average number of common shares outstanding - diluted (in shares)	368.0	376.8	370.9	378.7
Earnings per share available to IPG common stockholders:
Basic (in dollars per share)	$ 0.34	$ 0.05	$ 0.55	$ 0.92
Diluted (in dollars per share)	$ 0.34	$ 0.05	$ 0.54	$ 0.91