Summary of Significant Accounting Policies (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended			3 Months Ended			9 Months Ended		12 Months Ended
	Jun. 30, 2012	Jan. 31, 2012	Dec. 31, 2011	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Mar. 31, 2012	Nov. 30, 2011	May 31, 2011	Oct. 30, 2010
Reclassification and Revisions [Abstract]
Cumulative impact of prior period reclassification adjustment										$ 8,800,000
Impact of revision on cash flows									5,700,000
Variable Interest Entities [Abstract]
Number of collateralized debt obligations managed that meet the definition of a Variable Interest Entities due primarily to the lack of unilateral decision-making authority of the equity holders				5			5
Number of collateralized debt obligation's concluded that our investment management contract does not represent a variable interest				4			4
Cash of the variable interest entity				30,500,000			30,500,000
Collateral investments (at fair value) of the variable interest entity				298,000,000			298,000,000
Notes payable (at amortized cost) of the variable interest entity				317,100,000			317,100,000
Variable interests in certain structured products and hedge funds				22,300,000			22,300,000
Our maximum exposure to loss is limited to our investment in these entities				100,000			100,000
Investments [Abstract]
Limited Partnership Interest in Venture Capital Fund (in hundredths)							10.00%
Private equity investments owned outside of consolidated venture capital fund							2
Private equity investments owned outside consolidated venture capital fund accounted for using cost method							1
Goodwill [Abstract]
Purchase price for SCB, Inc., cash payment portion				1,500,000,000			1,500,000,000				15,000,000	5,500,000	14,300,000
Purchase price SCB, Inc., AllianceBernstein units issued (in units)							40.8
Goodwill amount				3,000,000,000			3,000,000,000				9,800,000	5,700,000	46,100,000
Holding units on unadjusted basis AllianceBernstein's fair value per unit (in dollars per value)				$ 15.41			$ 15.41
AllianceBernstein's carrying value per unit (in dollars per value)				$ 14.09			$ 14.09
Discount expected cash flow model used by management's for years of business plan				5 years			5 years
Expected distribution of the earnings (in hundredths)				100.00%			100.00%
Stress levels percentage of growth rates (in hundredths)				50.00%			50.00%
Fair value exceeds carrying value using market approach (in hundredths)				9.00%			9.00%
Fair value exceeds carrying value using income approach (in hundredths)				50.00%			50.00%
Intangible Assets, Net [Abstract]
Intangible assets, net of accumulated amortization			190,000,000	174,202,000	190,000,000		174,202,000		190,000,000
Definite-lived intangible assets subject to amortization, net				171,700,000			171,700,000
Indefinite-lived intangible assets not subject to amortization				2,500,000			2,500,000
Intangible assets acquired, estimated useful life							20 years
Gross carrying amount of intangible assets			424,700,000	425,100,000	424,700,000		425,100,000		424,700,000
Accumulated amortization of intangible assets			234,700,000	250,900,000	234,700,000		250,900,000		234,700,000
Net carrying amount of intangible assets			190,000,000	174,202,000	190,000,000		174,202,000		190,000,000
Amortization expense on intangible assets				5,467,000		5,443,000	16,146,000	16,174,000
Future estimated annual amortization expense [Abstract]
2012				22,000,000			22,000,000
2013				22,000,000			22,000,000
2014				22,000,000			22,000,000
2015				22,000,000			22,000,000
2016				22,000,000			22,000,000
Deferred Sales Commissions, Net [Abstract]
Period of time the deferred sales commissions are amortized over for U.S. fund shares				5 years 6 months			5 years 6 months
Period of time the deferred sales commissions are amortized over for non-U.S. fund shares				4 years			4 years
Deferred Compensation Plans [Abstract]
Deferred awards vesting period							4 years
Employee allocation percentage maximum (in hundredths)			50.00%		50.00%				50.00%
Deferred cash maximum per employee			250,000		250,000				250,000
Number of business days used in calculation		5 days
Non-cash deferred compensation charge					587,100,000
Deferred compensation liability for the full dollar value of the awards			159,900,000		159,900,000				159,900,000
Reclassified liability to partners' capital		130,300,000
Percentage of unrecognized deferred incentive compensation expense recognized (in hundredths)			100.00%		100.00%				100.00%
Holding Units purchased in periods (in units)				2.9			9.5
Dollar amount paid for Holding Units acquired				39,800,000			134,900,000
Open-market purchases of Holding Units (in units)				2.8			9.2
Dollar amount paid for open-market purchases of Holding Units				38,800,000			129,400,000
Restricted Holding Units awarded to employees (in units)	2.7	8.7	8.7				11.9
Unallocated Holding Units remaining in rabbi trust (in units)		8.7		11.8			11.8
Cash Distributions [Abstract]
Subsequent cash distribution, declaration date				Oct. 24, 2012
Subsequent cash distribution, amount				115,000,000
Subsequent cash distribution, distribution declared (in dollars per unit)				$ 0.41
General Partner partnership interest (in hundredths)				1.00%			1.00%
Subsequent cash distribution, distribution date				Nov. 21, 2012
Subsequent cash distribution, date of record				Nov. 05, 2012
Maximum [Member]
Goodwill [Abstract]
Fair value inputs, control premium (in hundredths)				20.00%
Fair value inputs, discount rate (in hundredths)				10.00%
Fair value inputs, long-term growth rate (in hundredths)				4.00%
Minimum [Member]
Goodwill [Abstract]
Fair value inputs, control premium (in hundredths)				10.00%
Fair value inputs, discount rate (in hundredths)				7.00%
Fair value inputs, long-term growth rate (in hundredths)				2.00%
Sanford C Bernstein Inc Acquisition [Member]
Goodwill [Abstract]
Goodwill amount				2,800,000,000			2,800,000,000
Intangible Assets, Net [Abstract]
Definite-lived intangible assets subject to amortization, net				165,600,000			165,600,000
Series of Individually Immaterial Business Acquisitions [Member]
Goodwill [Abstract]
Goodwill amount				$ 154,000,000			$ 154,000,000