Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenue	$ 1,884.9	$ 1,917.9	$ 3,638.8	$ 3,659.9
OPERATING EXPENSES:
Salaries and related expenses	1,239.3	1,229.5	2,514.7	2,498.3
Office and general expenses	439.1	464.1	887.9	914.3
Total operating expenses	1,678.4	1,693.6	3,402.6	3,412.6
OPERATING INCOME	206.5	224.3	236.2	247.3
EXPENSES AND OTHER INCOME:
Interest expense	(25.7)	(24.5)	(46.6)	(47.1)
Interest income	4.7	5.6	9.9	11.4
Other (expense) income, net	(15.4)	0.4	(14.6)	(18.8)
Total (expenses) and other income	(36.4)	(18.5)	(51.3)	(54.5)
Income before income taxes	170.1	205.8	184.9	192.8
Provision for income taxes	75.4	43.7	73.3	28.1
Income of consolidated companies	94.7	162.1	111.6	164.7
Equity in net (loss) income of unconsolidated affiliates	(0.1)	(1.9)	1.1	(1.8)
NET INCOME	94.6	160.2	112.7	162.9
Net loss (income) attributable to noncontrolling interests	0.1	(3.3)	3.5	(0.6)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 94.7	$ 156.9	$ 116.2	$ 162.3
Earnings per share, Basic	$ 0.24	$ 0.39	$ 0.30	$ 0.41
Earnings per share, Diluted	$ 0.24	$ 0.38	$ 0.29	$ 0.40
Weighted-average number of common shares outstanding, Basic	392.3	400.1	392.0	400.4
Weighted-average number of common shares outstanding, Diluted	400.3	409.8	399.6	409.4
Dividends declared per common share	$ 0.18	$ 0.15	$ 0.36	$ 0.30