Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
NET INCOME	$ 505.4	$ 288.9	$ 464.6
Other Comprehensive Income
Foreign currency translation adjustments, before tax	(194.3)	(116.9)	9.7
Less: reclassification adjustments recognized in net income	(0.9)	0	0
Foreign currency translation adjustments, income tax effect	0	(0.6)	0
Foreign currency translation adjustments, net of tax	(195.2)	(117.5)	9.7
Available-for-sale securities:
Changes in market value of available-for-sale securities	0.7	0.8	0.4
Less: recognition of previously unrealized (gains) losses included in net income	0	(1.4)	0.7
Available-for-sale securities, Income tax effect	(0.3)	0.2	(0.5)
Available-for-sale securities, Net of tax	0.4	(0.4)	0.6
Derivatives instruments:
Changes in fair value of derivative instruments	(0.6)	0	(21.9)
Less: recognition of previously unrealized losses included in net income	1.9	1.7	0.3
Derivative instruments, Income tax effect	(0.5)	(0.7)	8.9
Derivative instruments, Net of tax	0.8	1.0	(12.7)
Defined benefit pension and other postretirement plans:
Net actuarial losses for the period	(55.5)	(20.6)	(67.9)
Less: amortization of unrecognized losses, transition obligation and prior service cost included in net income	10.0	10.8	7.7
Less: settlement and curtailment losses (gains) included in net income	0.5	(0.1)	0.7
Other	0.5	1.0	(3.4)
Defined benefit pension and other postretirement plans, Income tax effect	10.4	(1.3)	1.9
Defined benefit pension and other postretirement plans, Net of tax	(34.1)	(10.2)	(61.0)
Other comprehensive loss, net of tax	(228.1)	(127.1)	(63.4)
Total comprehensive income	277.3	161.8	401.2
Less: comprehensive income attributable to noncontrolling interest	25.7	17.1	16.8
Comprehensive Income Attributable to IPG	$ 251.6	$ 144.7	$ 384.4