Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS									$ 618.9	$ 554.4	$ 605.0
Weighted-average number of common shares outstanding, Basic									383.3	389.6	397.9
Restricted stock, stock options and other equity awards									5.7	7.7	10.1
Weighted-average number of common shares outstanding, Diluted									389.0	397.3	408.0
Basic	$ 0.85	$ 0.42	$ 0.38	$ (0.04)	$ 0.66	$ 0.44	$ 0.27	$ 0.06	$ 1.61	$ 1.42	$ 1.52
Diluted	$ 0.84	$ 0.41	$ 0.37	$ (0.04)	$ 0.64	$ 0.43	$ 0.27	$ 0.06	$ 1.59	$ 1.40	$ 1.48