Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income available to IPG common stockholders - basic and diluted	$ 89.7	$ 45.4	$ 168.2	$ 66.1
Weighted Average Number of Shares Outstanding, Basic	419.2	419.7	421.0	419.7
Restricted stock, stock options and other equity awards, Effect of dilutive securities, Incremental common shares	7.2	6.4	6.2	5.1
Weighted Average Number of Shares Outstanding, Diluted	426.4	426.1	427.2	424.8
Earnings per share available to IPG common stockholders - basic	$ 0.21	$ 0.11	$ 0.40	$ 0.16
Earnings per share available to IPG common stockholders - diluted	$ 0.21	$ 0.11	$ 0.39	$ 0.16