Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
REVENUE	$ 7,882.4	$ 7,846.6	$ 7,613.8
OPERATING EXPENSES:
Salaries and related expenses	5,068.1	5,035.1	4,854.8
Office and general expenses	1,840.7	1,870.5	1,884.2
Total operating expenses	6,908.8	6,905.6	6,739.0
OPERATING INCOME	973.6	941.0	874.8
EXPENSES AND OTHER INCOME:
Interest expense	(90.8)	(90.6)	(85.8)
Interest income	19.4	20.1	22.8
Other expense, net	(26.2)	(40.3)	(49.6)
Total (expenses) and other income	(97.6)	(110.8)	(112.6)
Income before income taxes	876.0	830.2	762.2
Provision for income taxes	281.9	198.0	282.8
Income of consolidated companies	594.1	632.2	479.4
Equity in net income of unconsolidated affiliates	0.9	0.3	1.1
NET INCOME	595.0	632.5	480.5
Net income attributable to noncontrolling interests	(16.0)	(24.0)	(25.9)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 579.0	$ 608.5	$ 454.6
Earnings per share available to IPG common stockholders:
Basic	$ 1.49	$ 1.53	$ 1.11
Diluted	$ 1.46	$ 1.49	$ 1.09
Weighted-average number of common shares outstanding:
Basic	389.6	397.9	408.1
Diluted	397.3	408.0	415.7
Dividends declared per common share	$ 0.72	$ 0.60	$ 0.48