Net Income Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net Income - Omnicom Group Inc.	$ 203.9	$ 203.7	$ 691.2	$ 680.7
Net income allocated to participating securities	(4.5)	(2.3)	(15.4)	(7.3)
Net income available for common shares	$ 199.4	$ 201.4	$ 675.8	$ 673.4
Basic	266.6	277.1	269.6	279.8
Dilutive stock options and restricted shares	1.9	4.3	1.9	4.5
Diluted	268.5	281.4	271.5	284.3
Anti-dilutive stock options and restricted shares	0.2	2.1	0.2	1.6
Basic	$ 0.75	$ 0.73	$ 2.51	$ 2.41
Diluted	$ 0.74	$ 0.72	$ 2.49	$ 2.37

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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+ Details

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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-Name Regulation S-X (SX)

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+ Details

- Definition

The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

+ References+ Details

- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

+ References+ Details

- Definition

Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

+ References

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-URI http://asc.fasb.org/extlink&oid=6528421

+ Details