Earnings Per Share Basic and Diluted (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Mar. 31, 2010	Sep. 30, 2011	Sep. 30, 2010
Net income available to IPG common stockholders - basic	$ 208.1	$ 42.4		$ 261.7	$ 76.2
Net income available to IPG common stockholders - diluted	212.4	43.7		265.8	55.5
Weighted-average number of common shares outstanding - basic	464.7	474.7		471.3	473.0
Weighted-average number of common shares outstanding - diluted	537.6	533.6		527.8	526.4
Earnings per share available to IPG common stockholders - basic	$ 0.45	$ 0.09		$ 0.56	$ 0.16
Earnings per share available to IPG common stockholders - diluted	$ 0.40	$ 0.08		$ 0.50	$ 0.11
Adjustments: Effect of dilutive securities
Preferred stock dividends	2.9	0		0	0
Benefit from preferred stock repurchased	0	0		0	(21.7)	[1]
Add: Effect of dilutive securities
Restricted stock, stock options and other equity awards	7.6	10.6		7.7	9.3
Preferred stock outstanding	16.5	0		0	0
Preferred stock repurchased	0	0		0	11.9
Dividends declared and associated with preferred stock repurchased			4.0
4.25% Notes
Adjustments: Effect of dilutive securities
Interest on convertible debt	0.4	0.3		1.0	1.0
Add: Effect of dilutive securities
Convertible debt securities	32.5	32.2		32.5	32.2
Stated Interest Rate	4.25%			4.25%
4.75% Notes
Adjustments: Effect of dilutive securities
Interest on convertible debt	$ 1.0	$ 1.0		$ 3.1	$ 0
Add: Effect of dilutive securities
Convertible debt securities	16.3	16.1		16.3	0
Stated Interest Rate	4.75%			4.75%

[1] For the nine months ended September 30, 2010, the benefit from the preferred stock repurchased is excluded from net income available to IPG common stockholders for purposes of calculating diluted earnings per share since the associated common shares, if converted, were dilutive. In addition, the benefit is also net of $4.0 of preferred dividends that were declared during the first quarter of 2010 and associated with the preferred stock repurchased.