Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income available to IPG common stockholders									$ 608.5	$ 454.6	$ 477.1
Weighted-average number of common shares outstanding - basic									397.9	408.1	419.2
Restricted stock, stock options and other equity awards									10.1	7.6	6.2
Weighted-average number of common shares outstanding - diluted									408.0	415.7	425.4
Basic	$ 0.81	$ 0.32	$ 0.39	$ 0.01	$ 0.65	$ 0.18	$ 0.30	$ 0.00	$ 1.53	$ 1.11	$ 1.14
Diluted	$ 0.78	$ 0.32	$ 0.38	$ 0.01	$ 0.63	$ 0.18	$ 0.29	$ 0.00	$ 1.49	$ 1.09	$ 1.12