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Stock Option Valuation Assumptions (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |  |  |  |  |  |
Expected volatility | 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate | [1] | 40.20%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate | [1] | 43.80%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate | [1]
Expected term of share-based compensation awards | 0 years | [2] |  |  |  |
Expected term (years) |  |  | 6 years 11 months | [2] | 6 years 9 months | [2]
Risk free interest rate | 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate | [3] | 1.30%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate | [3] | 1.30%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate | [3]
Expected dividend yield | 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate | [4] | 2.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate | [4] | 2.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate | [4]
Annualized dividend per share used in calculation of expected dividend yield | $ 0.38ipg_AnnualizedDividendPerShareUsedInCalculationOfExpectedDividendYield |  | $ 0.30ipg_AnnualizedDividendPerShareUsedInCalculationOfExpectedDividendYield |  | $ 0.24ipg_AnnualizedDividendPerShareUsedInCalculationOfExpectedDividendYield |
[1] | The expected volatility used to estimate the fair value of stock options awarded is based on a blend of: (i) historical volatility of our common stock for periods equal to the expected term of our stock options and (ii) implied volatility of tradable forward put and call options to purchase and sell shares of our common stock.
[2] | The estimate of our expected term is based on the average of (i) an assumption that all outstanding options are exercised upon achieving their full vesting date and (ii) an assumption that all outstanding options will be exercised at the midpoint between the current date (i.e., the date awards have ratably vested through) and their full contractual term. In determining the estimate, we considered several factors, including the historical option exercise behavior of our employees and the terms and vesting periods of the options.
[3] | The risk free rate is determined using the implied yield currently available for zero-coupon U.S. government issuers with a remaining term equal to the expected term of the options.
[4] | The expected dividend yield is calculated based on an annualized dividend of $0.38 per share in 2014, $0.30 per share in 2013 and $0.24 per share in 2012.

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- Definition Annualized dividend per share used in calculation of expected dividend yield + References No definition available. + Details
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- Definition Expected term of share-based compensation awards + References No definition available. + Details
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- Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.D.2) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section D -Subsection 2 + Details
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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