Results by Quarter (Unaudited) Results by Quarter (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
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 2,063.3	$ 1,670.4		$ 1,715.7	$ 1,506.8	$ 2,072.6	$ 1,726.5	$ 1,740.7	$ 1,474.8	$ 6,956.2	$ 7,014.6	$ 6,507.3
Salaries and related expenses	1,133.8	1,064.3		1,088.9	1,104.9	1,138.3	1,088.0	1,095.7	1,080.1	4,391.9	4,402.1	4,117.0
Office and general expenses	519.6	474.7		450.4	441.3	549.0	465.3	471.0	440.0	1,886.0	1,925.3	1,841.6
Operating (loss) income	409.9	131.4		176.4	(39.4)	385.3	173.2	174.0	(45.3)	678.3	687.2	548.7
Other (expense) income, net	95.4	1.7	[1]	4.7	(1.3)	13.9	137.1	5.3	(6.1)	100.5	150.2	12.9
Total (expenses) and other income	66.9	(23.2)	[1]	(21.3)	(25.9)	(14.9)	113.9	(18.1)	(29.7)	(3.5)	51.2	(98.1)
(Benefit of) provision for income taxes	140.5	41.9		50.1	(19.2)	93.7	70.4	47.6	(21.5)	213.3	190.2	171.3
Net (loss) income	337.1	67.7	[1]	105.5	(45.7)	278.3	217.5	108.9	(53.2)	464.6	551.5	281.2
Net (loss) income available to IPG common stockholders	313.3	68.7	[1]	99.0	(45.9)	259.0	208.1	101.7	(48.1)	435.1	520.7	271.2
Earnings Per Share [Abstract]
Basic	$ 0.74	$ 0.16		$ 0.23	$ (0.10)	$ 0.58	$ 0.45	$ 0.21	$ (0.10)	$ 1.01	$ 1.12	$ 0.57
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 per common share	$ 0.06	$ 0.06		$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.24	$ 0.24	$ 0.00
Gain on sale of portion of Facebook										$ 93.6	$ 132.2

[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.