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, 2013	Sep. 30, 2013		Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Net income available to IPG common stockholders - basic	$ 193.1	$ 45.4	[1]	$ 79.9	$ (59.2)	$ 313.3	[1]	$ 68.7	$ 99.0	$ (45.9)	$ 259.2		$ 435.1		$ 520.7
Dividends on preferred stock											0		11.6		11.6
Net income available to IPG common stockholders - diluted											260.0		451.1		537.8
Weighted-average number of common shares outstanding - basic											421.1		432.5		465.5
Restricted stock, stock options and other equity awards											5.2		7.2		9.1
Preferred stock outstanding 2											0	[2]	16.9		16.5
Weighted-average number of common shares outstanding - diluted											429.6		481.4		540.6
Earnings per share available to IPG common stockholders - basic	$ 0.45	$ 0.11		$ 0.19	$ (0.14)	$ 0.74		$ 0.16	$ 0.23	$ (0.10)	$ 0.62		$ 1.01		$ 1.12
Earnings per share available to IPG common stockholders - diluted	$ 0.44	$ 0.11		$ 0.18	$ (0.14)	$ 0.68		$ 0.15	$ 0.22	$ (0.10)	$ 0.61		$ 0.94		$ 0.99
4.25% Convertible Senior Notes due 2023
Interest on convertible debt											0	[3]	0.3	[3]	1.4
Convertible debt securities											0	[3]	7.9	[3]	33.0
4.75% Convertible Senior Notes due 2023
Interest on convertible debt											$ 0.8	[3]	$ 4.1	[3]	$ 4.1
Convertible debt securities											3.3	[3]	16.9	[3]	16.5

[1] The three months ended September 30, 2013 include a pre-tax loss of $45.2, related to our early extinguishment of debt. The three months ended December 31, 2012 include a pre-tax gain of $93.6 related to the sale of our holdings in Facebook.

[2] We converted all of our Series B Preferred Stock into common stock in October 2013. See Note 3 for further information. For purposes of calculating diluted earnings per share for 2013, the potentially dilutive shares would have been pro-rated based on the period they were outstanding but were antidilutive.

[3] We retired all of our outstanding 4.75% Notes and 4.25% Notes in March 2013 and March 2012, respectively. See Note 2 for further information. For purposes of calculating diluted earnings per share for 2013 and 2012, the potentially dilutive shares are pro-rated based on the period they were outstanding.