Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenue	$ 1,917.9	$ 1,876.1	$ 3,659.9	$ 3,552.1
OPERATING EXPENSES:
Salaries and related expenses	1,229.0	1,205.2	2,499.9	2,420.4
Office and general expenses	464.1	455.1	914.3	908.1
Total operating expenses	1,693.1	1,660.3	3,414.2	3,328.5
OPERATING INCOME	224.8	215.8	245.7	223.6
EXPENSES AND OTHER INCOME:
Interest expense	(24.5)	(20.3)	(47.1)	(41.2)
Interest income	5.6	5.0	11.4	12.2
Other (expense) income, net	(0.1)	0.5	(17.2)	0.8
Total (expenses) and other income	(19.0)	(14.8)	(52.9)	(28.2)
Income before income taxes	205.8	201.0	192.8	195.4
Provision for income taxes	43.7	77.7	28.1	76.3
Income of consolidated companies	162.1	123.3	164.7	119.1
Equity in net (loss) income of unconsolidated affiliates	(1.9)	0.5	(1.8)	0.5
NET INCOME	160.2	123.8	162.9	119.6
Net income attributable to noncontrolling interests	(3.3)	(2.6)	$ (0.6)	$ (0.2)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 156.9	$ 121.2
Earnings per share, Basic	$ 0.39	$ 0.30	$ 0.41	$ 0.29
Earnings per share, Diluted	$ 0.38	$ 0.29	$ 0.40	$ 0.29
Weighted-average number of common shares outstanding, Basic	400.1	410.5	400.4	410.8
Weighted-average number of common shares outstanding, Diluted	409.8	417.6	409.4	417.6
Dividends declared per common share	$ 0.15	$ 0.12	$ 0.30	$ 0.24