Consolidated Statements of Operations (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
Income Statement [Abstract]
REVENUE	$ 1,756.2	$ 1,715.7	$ 3,299.2	$ 3,222.5
OPERATING EXPENSES:
Salaries and related expenses	1,120.2	1,088.9	2,252.3	2,193.8
Office and general expenses	461.2	450.4	914.5	891.7
Total operating expenses	1,581.4	1,539.3	3,166.8	3,085.5
OPERATING INCOME	174.8	176.4	132.4	137.0
EXPENSES AND OTHER INCOME:
Interest expense	(37.5)	(32.7)	(74.3)	(65.3)
Interest income	5.8	6.7	12.2	14.7
Other income, net	4.8	4.7	6.6	3.4
Total (expenses) and other income	(26.9)	(21.3)	(55.5)	(47.2)
Income before income taxes	147.9	155.1	76.9	89.8
Provision for income taxes	62.0	50.1	49.6	30.9
Income of consolidated companies	85.9	105.0	27.3	58.9
Equity in net income of unconsolidated affiliates	0.2	0.5	0.3	0.9
NET INCOME	86.1	105.5	27.6	59.8
Net income attributable to noncontrolling interests	(3.3)	(3.6)	(1.1)	(0.9)
NET INCOME ATTRIBUTABLE TO IPG	82.8	101.9	26.5	58.9
Dividends on preferred stock	(2.9)	(2.9)	(5.8)	(5.8)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 79.9	$ 99.0	$ 20.7	$ 53.1
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
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
Dividends declared per common share	$ 0.075	$ 0.060	$ 0.15	$ 0.12