Pension and Other Postemployment Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Contribution Plans [Abstract]
Defined contribution plans, contribution expense	$ 102.1	$ 83.9	$ 75.7
Fair Value of Plan Assets [Roll Forward]
Settlements	(5.4)	0
Level 3 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	6.1	5.6
Actual return on plan assets	0.1	0.1
Purchases, sales, and settlements, net	(4.5)	0.4
Fair value of assets December 31	1.7	6.1
Defined Benefit Pension Plans [Member]
Defined Contribution Plans [Abstract]
Defined benefit plans, plan information	Certain of our subsidiaries sponsor noncontributory defined benefit pension plans. Two of our U.S. businesses and several of our non-U.S. businesses sponsor pension plans. These plans provide benefits to employees based on formulas recognizing length of service and earnings. The U.S. plans cover approximately 1,200 participants and are closed to new participants. Effective January 1, 2011, the U.S. plans do not accrue future benefit credits. The non-U.S. plans cover approximately 6,500 participants, are not covered by ERISA and include plans required by local laws.
Components of Net Periodic Benefit Cost [Abstract]
Service cost	5.8	3.9	4.4
Interest cost	6.5	6.1	6.7
Expected return on plan assets	(3.5)	(3.5)	(3.6)
Amortization of prior service cost	3.1	2.5	2.5
Amortization of actuarial (gains) losses	0.3	0.6	1.6
Curtailments and settlements	0	1.2	1.4
Net periodic benefit cost	12.2	10.8	13.0
Amounts Recognized in Accumulated Other Comprehensive Income [Abstract]
Unrecognized actuarial gains and losses and unrecognized prior service cost	66.2	44.7
Unrecognized actuarial gains and losses and unrecognized prior service cost, net of tax	41.2	27.5
Unrecognized actuarial gains and losses expected to be amortized in the next year	4.6
Weighted Average Assumptions Used to Determine the Net Periodic Benefit Cost [Abstract]
Net periodic benefit cost, Discount rate	5.10%	5.60%	5.60%
Net periodic benefit cost, Discount rateCompensation increases	1.60%	2.30%	2.10%
Net periodic benefit cost, Discount rateExpected return on plan assets	6.20%	6.70%	6.40%
Defined benefit pension plans, contributions by employer	7.8	7.5	6.4
Benefit Obligation [Roll Forward]
Benefit obligation January 1	130.0	120.9
Service cost	5.8	3.9	4.4
Interest cost	6.5	6.1	6.7
Plan amendments, curtailments and settlements	(13.6)	2.6
Actuarial (gains) losses	23.1	7.2
Benefits paid	(5.1)	(10.3)
Foreign currency translation	(0.4)	(0.4)
Benefit obligation December 31	146.3	130.0	120.9
Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	53.9	52.4
Actual return on plan assets	(0.6)	4.5
Employer contributions	7.8	7.5	6.4
Benefits paid	(5.1)	(10.3)
Foreign currency translation	(0.1)	(0.2)
Fair value of assets December 31	50.5	53.9	52.4
Funded Status [Abstract]
Funded Status December 31	(95.8)	(76.1)
Amounts Recorded in Balance Sheet [Abstract]
Other assets	1.9	3.0
Other current liabilities	(1.3)	(1.1)
Long-term liabilities	(96.4)	(78.0)
Total amount recognized in balance sheet	95.8	76.1
Accumulated benefit obligation	135.8	119.2
Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Plans with benefit obligations in excess of plan assets, Benefit obligation	136.4	114.1
Plans with benefit obligations in excess of plan assets, Plan assets	38.7	35.0
Plans with benefit obligations in excess of plan assets, Liabilities	97.7	79.1
Weighted Average Assumptions Used to Determine Benefit Obligation [Abstract]
Benefit obligation, Discount rate	4.60%	5.00%
Benefit obligation, Compensation increases	1.40%	1.90%
Estimated Future Benefit Payments [Abstract]
Estimated future benefit payments, 2012	4.1
Estimated future benefit payments, 2013	4.9
Estimated future benefit payments, 2014	7.7
Estimated future benefit payments, 2015	5.5
Estimated future benefit payments, 2016	5.8
Estimated future benefit payments, 2017-2021	41.4
Estimated future benefit payments, Thereafter	76.9
Estimated future benefit payments	146.3
Weighted Average Asset Allocations [Abstract]
Target Allocation Percentage of Plan Assets	100.00%
Actual Allocation Percentage of Plan Assets	100.00%	100.00%
Defined Benefit Pension Plans [Member] | Level 1 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	48.6	44.7
Defined Benefit Pension Plans [Member] | Level 2 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	0.2	3.1
Defined Benefit Pension Plans [Member] | Level 3 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	1.7	6.1
Defined Benefit Pension Plans [Member] | Cash and Cash Equivalents [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	1.0
Fair value of assets December 31	1.6
Weighted Average Asset Allocations [Abstract]
Target Allocation Percentage of Plan Assets	2.00%
Actual Allocation Percentage of Plan Assets	3.00%	2.00%
Defined Benefit Pension Plans [Member] | Cash and Cash Equivalents [Member] | Level 1 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	1.6	1.0
Defined Benefit Pension Plans [Member] | Mutual Funds [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	24.9
Fair value of assets December 31	29.7
Estimated Future Benefit Payments [Abstract]
Percentage of plan assets, equity funds	67.00%	63.00%
Percentage of plan assets, debt funds	33.00%	37.00%
Weighted Average Asset Allocations [Abstract]
Target Allocation Percentage of Plan Assets	55.00%
Actual Allocation Percentage of Plan Assets	59.00%	46.00%
Defined Benefit Pension Plans [Member] | Mutual Funds [Member] | Level 1 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	29.7	24.9
Defined Benefit Pension Plans [Member] | Unit Trusts [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	18.8
Fair value of assets December 31	17.3
Estimated Future Benefit Payments [Abstract]
Percentage of plan assets, equity funds	46.00%	54.00%
Percentage of plan assets, debt funds	54.00%	46.00%
Weighted Average Asset Allocations [Abstract]
Target Allocation Percentage of Plan Assets	37.00%
Actual Allocation Percentage of Plan Assets	34.00%	35.00%
Defined Benefit Pension Plans [Member] | Unit Trusts [Member] | Level 1 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	17.3	18.8
Defined Benefit Pension Plans [Member] | Insurance Contracts [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	6.1
Fair value of assets December 31	1.7
Weighted Average Asset Allocations [Abstract]
Target Allocation Percentage of Plan Assets	3.00%
Actual Allocation Percentage of Plan Assets	3.00%	11.00%
Defined Benefit Pension Plans [Member] | Insurance Contracts [Member] | Level 1 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	0	0
Defined Benefit Pension Plans [Member] | Insurance Contracts [Member] | Level 3 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	1.7	6.1
Defined Benefit Pension Plans [Member] | Other Plan Assets [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	3.1
Fair value of assets December 31	0.2
Weighted Average Asset Allocations [Abstract]
Target Allocation Percentage of Plan Assets	3.00%
Actual Allocation Percentage of Plan Assets	1.00%	6.00%
Defined Benefit Pension Plans [Member] | Other Plan Assets [Member] | Level 1 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	0	0
Defined Benefit Pension Plans [Member] | Other Plan Assets [Member] | Level 2 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	0.2	3.1
Defined Benefit Pension Plans [Member] | Other Plan Assets [Member] | Level 3 [Member]
Fair Value of Plan Assets [Roll Forward]
Fair value of assets December 31	0	0
Retention Plan [Member]
Defined Contribution Plans [Abstract]
Defined benefit plans, plan information	In addition, we have a Senior Executive Restrictive Covenant and Retention Plan (“Retention Plan”) for certain executive officers of Omnicom selected to participate by the Compensation Committee. The Retention Plan was adopted to secure non-competition, non-solicitation, non-disparagement and ongoing consulting services from such executive officers, and to strengthen the retention aspect of executive officer compensation. The Retention Plan provides for annual payments to the participants or to their beneficiaries upon termination following at least seven years of service with Omnicom or its subsidiaries. A participant’s annual benefit is payable for 15 consecutive calendar years following termination, but in no event prior to age 55. The annual benefit is equal to the lesser of (i) the participant’s final average pay times an applicable percentage, which is based upon the executive’s years of service as an executive officer, not to exceed 35% or (ii) $1.5 million. The Retention Plan is unfunded and benefits will be paid when due.
Postemployment Arrangements [Member]
Defined Contribution Plans [Abstract]
Defined benefit plans, plan information	We have executive retirement agreements under which benefits will be paid to participants or to their beneficiaries over periods up to 10 years beginning after cessation of full-time employment. Our postemployment arrangements are unfunded and benefits are paid when due.
Components of Net Periodic Benefit Cost [Abstract]
Service cost	3.9	1.8	1.8
Interest cost	4.7	3.9	4.0
Amortization of prior service cost	0.6	0.6	0.8
Amortization of actuarial (gains) losses	2.1	1.0	0.5
Net periodic benefit cost	11.3	7.3	7.1
Amounts Recognized in Accumulated Other Comprehensive Income [Abstract]
Unrecognized actuarial gains and losses and unrecognized prior service cost	44.9	45.0
Unrecognized actuarial gains and losses and unrecognized prior service cost, net of tax	26.9	27.0
Unrecognized actuarial gains and losses expected to be amortized in the next year	2.0
Weighted Average Assumptions Used to Determine the Net Periodic Benefit Cost [Abstract]
Net periodic benefit cost, Discount rate	5.00%	5.00%	5.30%
Net periodic benefit cost, Discount rateCompensation increases	3.50%	3.50%	3.50%
Benefit Obligation [Roll Forward]
Benefit obligation January 1	104.7	87.7
Service cost	3.9	1.8	1.8
Interest cost	4.7	3.9	4.0
Plan amendments, curtailments and settlements	0	20.4
Actuarial (gains) losses	2.6	0.9
Benefits paid	(10.7)	(10.0)
Benefit obligation December 31	105.2	104.7	87.7
Fair Value of Plan Assets [Roll Forward]
Benefits paid	(10.7)	(10.0)
Amounts Recorded in Balance Sheet [Abstract]
Other current liabilities	(10.2)	(10.7)
Long-term liabilities	(95.0)	(94.0)
Total amount recognized in balance sheet	105.2	104.7
Weighted Average Assumptions Used to Determine Benefit Obligation [Abstract]
Benefit obligation, Discount rate	4.90%	5.00%
Benefit obligation, Compensation increases	3.50%	3.50%
Estimated Future Benefit Payments [Abstract]
Estimated future benefit payments, 2012	10.2
Estimated future benefit payments, 2013	9.8
Estimated future benefit payments, 2014	8.3
Estimated future benefit payments, 2015	7.2
Estimated future benefit payments, 2016	7.5
Estimated future benefit payments, 2017-2021	28.1
Estimated future benefit payments, Thereafter	$ 34.1