Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011
Net income available to IPG common stockholders - basic	$ 68.7		$ 208.1	$ 121.8		$ 261.7
Preferred stock dividends	0		2.9	0		0
Net income available to IPG common stockholders - diluted	69.7		212.4	125.2		265.8
Weighted-average number of common shares outstanding - basic	431.3		464.7	435.5		471.3
Restricted stock, stock options and other equity awards	8.1		7.6	7.1		7.7
Preferred stock outstanding	0		16.5	0		0
Weighted-average number of common shares outstanding - diluted	456.1		537.6	469.7		527.8
Earnings per share available to IPG common stockholders - basic	$ 0.16		$ 0.45	$ 0.28		$ 0.56
Earnings per share available to IPG common stockholders - diluted	$ 0.15		$ 0.40	$ 0.27		$ 0.50
4.25% Notes
Interest on convertible debt	0		0.4	0.3		1.0
Convertible debt securities	0	[1]	32.5	10.4	[1]	32.5
4.75% Notes
Interest on convertible debt	$ 1.0		$ 1.0	$ 3.1		$ 3.1
Convertible debt securities	16.7		16.3	16.7		16.3

[1] We retired all of our outstanding 4.25% Notes in March 2012. For purposes of calculating diluted earnings per share for the first nine months of 2012, the potentially dilutive shares are pro-rated based on the period they were outstanding.