Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011
Net income available to IPG common stockholders - basic	$ 99.0		$ 101.7	$ 53.1		$ 53.6
Preferred stock dividends	2.9		2.9	0		0
Net income available to IPG common stockholders - diluted	102.9		106.0	53.4		54.3
Weighted-average number of common shares outstanding - basic	437.4		473.1	437.5		474.6
Restricted stock, stock options and other equity awards	6.9		8.8	6.6		8.5
Preferred stock outstanding	16.7		16.2	0		0
Weighted-average number of common shares outstanding - diluted	477.7		546.9	459.7		515.6
Earnings per share available to IPG common stockholders - basic	$ 0.23		$ 0.21	$ 0.12		$ 0.11
Earnings per share available to IPG common stockholders - diluted	$ 0.22		$ 0.19	$ 0.12		$ 0.11
4.25% Notes
Interest on convertible debt	0		0.4	0.3		0.7
Convertible debt securities	0	[1]	32.5	15.6	[1]	32.5
4.75% Notes
Interest on convertible debt	$ 1.0		$ 1.0	$ 0		$ 0
Convertible debt securities	16.7		16.3	0		0

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