Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenue	$ 1,902.6	$ 1,922.2	$ 5,541.4	$ 5,582.1
OPERATING EXPENSES:
Salaries and related expenses	1,227.6	1,228.0	3,742.3	3,726.3
Office and general expenses	455.9	486.2	1,343.8	1,400.5
Total operating expenses	1,683.5	1,714.2	5,086.1	5,126.8
OPERATING INCOME	219.1	208.0	455.3	455.3
EXPENSES AND OTHER INCOME:
Interest expense	(21.0)	(21.7)	(67.6)	(68.8)
Interest income	4.1	4.7	14.0	16.1
Other (expense) income, net	(9.9)	5.3	(24.5)	(13.5)
Total (expenses) and other income	(26.8)	(11.7)	(78.1)	(66.2)
Income before income taxes	192.3	196.3	377.2	389.1
Provision for income taxes	42.5	63.8	115.8	91.9
Income of consolidated companies	149.8	132.5	261.4	297.2
Equity in net (loss) income of unconsolidated affiliates	(1.0)	0.2	0.1	(1.6)
NET INCOME	148.8	132.7	261.5	295.6
Net (income) loss attributable to noncontrolling interests	(2.6)	(4.1)	0.9	(4.7)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 146.2	$ 128.6	$ 262.4	$ 290.9
Earnings per share, Basic	$ 0.38	$ 0.32	$ 0.67	$ 0.73
Earnings per share, Diluted	$ 0.37	$ 0.32	$ 0.66	$ 0.71
Weighted-average number of common shares outstanding, Basic	389.5	397.7	391.2	399.5
Weighted-average number of common shares outstanding, Diluted	397.2	407.9	398.6	408.8
Dividends declared per common share	$ 0.18	$ 0.15	$ 0.54	$ 0.45