Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income available to IPG common stockholders	$ 128.6	$ 74.9	$ 290.9	$ 194.3
Weighted-average number of common shares outstanding, Basic	397.7	407.6	399.5	409.7
Restricted stock, stock options and other equity awards	10.2	7.9	9.3	7.3
Weighted-average number of common shares outstanding, Diluted	407.9	415.5	408.8	417.0
Earnings per share, Basic	$ 0.32	$ 0.18	$ 0.73	$ 0.47
Earnings per share, Diluted	$ 0.32	$ 0.18	$ 0.71	$ 0.47