Earnings Per Share Basic and Diluted (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010		Mar. 31, 2010	Jun. 30, 2011	Jun. 30, 2010
Net income available to IPG common stockholders - basic	$ 101.7	$ 105.3			$ 53.6	$ 33.8
Net income available to IPG common stockholders - diluted	106.0	81.0			54.3	12.8
Weighted-average number of common shares outstanding - basic	473.1	473.0			474.6	472.1
Weighted-average number of common shares outstanding - diluted	546.9	544.9			515.6	531.6
Earnings per share available to IPG common stockholders - basic	$ 0.21	$ 0.22			$ 0.11	$ 0.07
Earnings per share available to IPG common stockholders - diluted	$ 0.19	$ 0.15			$ 0.11	$ 0.02
Adjustments: Effect of dilutive securities
Preferred stock dividends	2.9	0			0	0
Benefit from preferred stock repurchased	0	(25.7)	[1]		0	(21.7)	[1]
Add: Effect of dilutive securities
Restricted stock, stock options and other equity awards	8.8	9.8			8.5	9.3
Preferred stock outstanding	16.2	0			0	0
Preferred stock repurchased	0	13.8			0	18.0
Dividends declared and associated with preferred stock repurchased				4.0
4.25% Notes
Adjustments: Effect of dilutive securities
Interest on convertible debt	0.4	0.4			0.7	0.7
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			$ 0	$ 0
Add: Effect of dilutive securities
Convertible debt securities	16.3	16.1			0	0
Stated Interest Rate	4.75%				4.75%

[1] For the three and six months ended June 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, for the six months ended June 30, 2010, 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.