Consolidated Statements of Operations (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]
REVENUE	$ 1,700.4	$ 1,670.4	$ 4,999.6	$ 4,892.9
OPERATING EXPENSES:
Salaries and related expenses	1,093.6	1,064.3	3,345.9	3,258.1
Office and general expenses	465.3	474.7	1,379.8	1,366.4
Total operating expenses	1,558.9	1,539.0	4,725.7	4,624.5
OPERATING INCOME	141.5	131.4	273.9	268.4
EXPENSES AND OTHER INCOME:
Interest expense	(23.7)	(31.6)	(98.0)	(96.9)
Interest income	5.8	6.7	18.0	21.4
Other (expense) income, net	(46.6)	1.7	(40.0)	5.1
Total (expenses) and other income	(64.5)	(23.2)	(120.0)	(70.4)
Income before income taxes	77.0	108.2	153.9	198.0
Provision for income taxes	28.4	41.9	78.0	72.8
Income of consolidated companies	48.6	66.3	75.9	125.2
Equity in net income of unconsolidated affiliates	0.6	1.4	0.9	2.3
NET INCOME	49.2	67.7	76.8	127.5
Net (income) loss attributable to noncontrolling interests	(0.9)	3.9	(2.0)	3.0
NET INCOME ATTRIBUTABLE TO IPG	48.3	71.6	74.8	130.5
Dividends on preferred stock	(2.9)	(2.9)	(8.7)	(8.7)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 45.4	$ 68.7	$ 66.1	$ 121.8
Earnings per share available to IPG common stockholders, Basic	$ 0.11	$ 0.16	$ 0.16	$ 0.28
Earnings per share available to IPG common stockholders, Diluted	$ 0.11	$ 0.15	$ 0.16	$ 0.27
Weighted-average number of common shares outstanding, Basic	419.7	431.3	419.7	435.5
Weighted-average number of common shares outstanding, Diluted	426.1	456.1	424.8	469.7
Dividends declared per common share	$ 0.075	$ 0.060	$ 0.225	$ 0.180