Accumulated Other Comprehensive Loss, net of tax Changes in AOCI (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Changes in market value of available-for-sale securities	$ 0.7	$ 0.8	$ 0.4
Changes in fair value of derivative instruments	(0.6)	0	(21.9)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	(246.6)	(131.9)
Total Reclassification from AOCI	21.1ipg_TotalReclassificationfromAOCI	8.7ipg_TotalReclassificationfromAOCI	19.7ipg_TotalReclassificationfromAOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax	(636.7)	(411.2)	(288.0)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign Currency Transaction and Translation Gain (Loss), before Reclassification and Tax	(191.7)	(113.0)
Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	(0.9)	(0.6)
Foreign Currency Translation Adjustment, Net of Tax	(436.3)	(243.7)	(130.1)
Available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Changes in market value of available-for-sale securities	0.7	0.8
Available-for-sale Securities Adjustment, Net of Tax	0.8	0.4	0.8
Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(0.3)	(1.2)
Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Changes in fair value of derivative instruments	(0.6)	0
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	1.4	1.0
Cumulative Changes in Net Gain (Loss) from Hedges, Effect Net of Tax	(10.9)	(11.7)	(12.7)
Defined Benefit and Postretirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension and Other Postretirement Benefit Plans, Adjustment, before Reclassification Adjustments and Tax	(55.0)	(19.7)
Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	20.9	9.5
Pension and Other Postretirement Benefit Plans, Net of Tax	$ 190.3	$ (156.2)	$ (146.0)

Total Reclassification from AOCI

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Accumulated change, net of tax, in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Includes an entity's share of an equity investee's Increase or Decrease in deferred hedging gains or losses.

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The total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

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Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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Amount before tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount before tax of other comprehensive income (loss) attributable to parent entity.

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