Earnings Per Share Basic and Diluted (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Net income available to IPG common stockholders - basic	$ 313.3	$ 68.7	[1]	$ 99.0	$ (45.9)	$ 259.0	$ 208.1	$ 101.7	$ (48.1)	$ 435.1		$ 520.7	$ 271.2
Preferred stock dividends										11.6		11.6	0
Benefit from preferred stock repurchased										0		0	(21.7)	[2]
Net income available to IPG common stockholders - diluted										451.1		537.8	254.9
Weighted-average number of common shares outstanding - basic										432.5		465.5	473.6
Restricted stock, stock options and other equity awards										7.2		9.1	11.3
Preferred stock outstanding										16.9		16.5	0
Preferred stock repurchased										0		0	8.9
Weighted-average number of common shares outstanding - diluted										481.4		540.6	542.1
Earnings per share available to IPG common stockholders - basic	$ 0.74	$ 0.16		$ 0.23	$ (0.10)	$ 0.58	$ 0.45	$ 0.21	$ (0.10)	$ 1.01		$ 1.12	$ 0.57
Earnings per share available to IPG common stockholders - diluted	$ 0.68	$ 0.15		$ 0.22	$ (0.10)	$ 0.50	$ 0.40	$ 0.19	$ (0.10)	$ 0.94		$ 0.99	$ 0.47
Dividends declared and associated with preferred stock repurchased													4.0
4.25% Notes
Interest on convertible debt										0.3	[3]	1.4	1.4
Convertible debt securities										7.9	[3]	33.0	32.2
4.75% Notes
Interest on convertible debt										$ 4.1		$ 4.1	$ 4.0
Convertible debt securities										16.9		16.5	16.1

[1] The three months ended December 31, 2012 and the three months ended September 30, 2011, include a pre-tax gain of $93.6 and $132.2, respectively, related to the sale of our holdings in Facebook.

[2] For the year ended December 31, 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.

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