Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Net income available to IPG common stockholders, Basic	$ 79.9		$ 99.0		$ 20.7		$ 53.1
Net income available to IPG common stockholders, Diluted	82.8		102.9		20.7		53.4
Weighted-average number of common shares outstanding, Basic	425.1		437.4		419.7		437.5
Weighted-average number of common shares outstanding, Diluted	448.3		477.7		425.1		459.7
Earnings per share available to IPG common stockholders, Basic	$ 0.19		$ 0.23		$ 0.05		$ 0.12
Earnings per share available to IPG common stockholders, Diluted	$ 0.18		$ 0.22		$ 0.05		$ 0.12
Preferred stock dividends, Effect of dilutive securities	2.9		2.9		0		0
Restricted stock, stock options and other equity awards, Effect of dilutive securities, Incremental common shares	6.1		6.9		5.4		6.6
Preferred stock outstanding, Effect of dilutive securities, Incremental common shares	17.1		16.7		0		0
4.75% Notes
Interest on convertible debt, Effect of dilutive securities	0	[1]	1.0		0	[1]	0
Convertible debt, Effect of dilutive securities, Incremental common shares	0	[1]	16.7		0	[1]	0
4.25% Notes
Interest on convertible debt, Effect of dilutive securities	$ 0		$ 0	[2]	$ 0		$ 0.3	[2]
Convertible debt, Effect of dilutive securities, Incremental common shares	0		0	[2]	0		15.6	[2]

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

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