Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net revenue	$ 1,774.0	$ 1,675.3
Billable expense	395.1	388.5
Total revenue	2,169.1	2,063.8
OPERATING EXPENSES:
Salaries and related expenses	1,330.3	1,251.7
Office and other direct expenses	323.8	312.7
Billable expenses	395.1	388.5
Cost of services	2,049.2	1,952.9
Selling, general and administrative expenses	35.1	35.2
Depreciation and amortization	46.0	41.0
Total operating expenses	2,130.3	2,029.1
OPERATING INCOME	38.8	34.7
EXPENSES AND OTHER INCOME:
Interest expense	(19.9)	(20.9)
Interest income	4.0	5.2
Other (expense) income, net	(24.4)	0.8
Total (expenses) and other income	(40.3)	(14.9)
(Loss) income before income taxes	(1.5)	19.8
Provision for (benefit of) income taxes	12.7	(0.3)
(Loss) income of consolidated companies	(14.2)	20.1
Equity in net (loss) income of unconsolidated affiliates	(1.9)	1.2
NET (LOSS) INCOME	(16.1)	21.3
Net loss attributable to noncontrolling interests	2.0	3.4
NET (LOSS) INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ (14.1)	$ 24.7
Earnings per share, Basic	$ (0.04)	$ 0.06
Earnings per share, Diluted	$ (0.04)	$ 0.06
Weighted-average number of common shares outstanding, Basic	383.4	391.7
Weighted-average number of common shares outstanding, Diluted	383.4	399.3
Dividends declared per common share	$ 0.21	$ 0.18