Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Revenue	$ 1,922.2	$ 1,865.5	$ 5,582.1	$ 5,417.6
OPERATING EXPENSES:
Salaries and related expenses	1,228.8	1,202.2	3,728.7	3,622.6
Office and general expenses	486.2	471.4	1,400.5	1,379.5
Total operating expenses	1,715.0	1,673.6	5,129.2	5,002.1
OPERATING INCOME	207.2	191.9	452.9	415.5
EXPENSES AND OTHER INCOME:
Interest expense	(21.7)	(21.3)	(68.8)	(62.5)
Interest income	4.7	5.6	16.1	17.8
Other income (expense), net	6.1	(37.2)	(11.1)	(36.4)
Total (expenses) and other income	(10.9)	(52.9)	(63.8)	(81.1)
Income before income taxes	196.3	139.0	389.1	334.4
Provision for income taxes	63.8	61.1	91.9	137.4
Income of consolidated companies	132.5	77.9	297.2	197.0
Equity in net income (loss) of unconsolidated affiliates	0.2	0.1	(1.6)	0.6
NET INCOME	132.7	78.0	295.6	197.6
Net income attributable to noncontrolling interests	(4.1)	(3.1)	(4.7)	(3.3)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 128.6	$ 74.9	$ 290.9	$ 194.3
Earnings per share, Basic	$ 0.32	$ 0.18	$ 0.73	$ 0.47
Earnings per share, Diluted	$ 0.32	$ 0.18	$ 0.71	$ 0.47
Weighted-average number of common shares outstanding, Basic	397.7	407.6	399.5	409.7
Weighted-average number of common shares outstanding, Diluted	407.9	415.5	408.8	417.0
Dividends declared per common share	$ 0.15	$ 0.12	$ 0.45	$ 0.36