Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
NET INCOME	$ 595.0	$ 632.5	$ 480.5
Foreign Currency Translation:
Foreign currency translation adjustments	132.2	(55.9)	(256.8)
Reclassification adjustments recognized in net income	1.1	3.7	23.3
Foreign currency translation, net of tax	133.3	(52.2)	(233.5)
Available-for-sale securities:
Changes in fair value of available-for-sale securities	0.0	0.5	0.5
Recognition of previously unrealized gains in net income	(0.7)	(1.3)	0.0
Income tax effect	0.1	0.1	0.0
Available-for-sale securities, net of tax	(0.6)	(0.7)	0.5
Derivatives instruments:
Recognition of previously unrealized losses included in net income	2.1	2.0	2.0
Income tax effect	(0.5)	(0.8)	(0.7)
Derivative instruments, net of tax	1.6	1.2	1.3
Defined benefit pension and other postretirement plans:
Net actuarial (losses) gains for the period	(13.6)	(85.4)	14.2
Amortization of unrecognized losses, transition obligation and prior service cost included in net income	6.9	5.4	10.6
Less: settlement and curtailment losses (gains) included in net income	6.8	0.4	(0.2)
Other	2.7	(2.0)	0.4
Income tax effect	(0.5)	15.3	(6.4)
Defined benefit pension and other postretirement plans, net of tax	2.3	(66.3)	18.6
Other comprehensive income (loss), net of tax	136.6	(118.0)	(213.1)
Total comprehensive income	731.6	514.5	267.4
Less: comprehensive income attributable to noncontrolling interests	17.5	22.9	21.7
Comprehensive Income Attributable to IPG	$ 714.1	$ 491.6	$ 245.7