Consolidated Statements of Operations (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Income Statement [Abstract]
REVENUE	$ 1,670.4	$ 1,726.5	$ 4,892.9	$ 4,942.0
OPERATING EXPENSES:
Salaries and related expenses	1,064.3	1,088.0	3,258.1	3,263.8
Office and general expenses	474.7	465.3	1,366.4	1,376.3
Total operating expenses	1,539.0	1,553.3	4,624.5	4,640.1
OPERATING INCOME	131.4	173.2	268.4	301.9
EXPENSES AND OTHER INCOME:
Interest expense	(31.6)	(32.9)	(96.9)	(97.9)
Interest income	6.7	9.7	21.4	27.7
Other income, net	1.7	137.1	5.1	136.3
Total (expenses) and other income	(23.2)	113.9	(70.4)	66.1
Income before income taxes	108.2	287.1	198.0	368.0
Provision for income taxes	41.9	70.4	72.8	96.5
Income of consolidated companies	66.3	216.7	125.2	271.5
Equity in net income of unconsolidated affiliates	1.4	0.8	2.3	1.7
NET INCOME	67.7	217.5	127.5	273.2
Net loss (income) attributable to noncontrolling interests	3.9	(6.5)	3.0	(2.8)
NET INCOME ATTRIBUTABLE TO IPG	71.6	211.0	130.5	270.4
Dividends on preferred stock	(2.9)	(2.9)	(8.7)	(8.7)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 68.7	$ 208.1	$ 121.8	$ 261.7
Earnings per share available to IPG common stockholders:
Basic	$ 0.16	$ 0.45	$ 0.28	$ 0.56
Diluted	$ 0.15	$ 0.40	$ 0.27	$ 0.50
Weighted-average number of common shares outstanding:
Basic	431.3	464.7	435.5	471.3
Diluted	456.1	537.6	469.7	527.8
Dividends declared per common share	$ 0.06	$ 0.06	$ 0.18	$ 0.18