Debt (Details) (USD $)	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	1 Months Ended		9 Months Ended	12 Months Ended	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Commercial Paper [Member]	Dec. 31, 2011 Commercial Paper [Member]	Jul. 13, 2012 Line of Credit [Member]	Jan. 17, 2012 Line of Credit [Member]	Sep. 30, 2012 Line of Credit [Member]	Dec. 31, 2011 Line of Credit [Member]	Sep. 30, 2012 Line of Credit [Member] Subsidiaries [Member]	Sep. 30, 2012 Uncommited Lines of Credit [Member]	May 31, 2012 Uncommited Lines of Credit [Member]
Short-term Debt [Line Items]
Short-term debt outstanding	$ 241,337,000	$ 444,903,000	$ 241,300,000	$ 444,900,000
Weighted average interest rates on short-term debt outstanding (in hundredths)			0.50%	0.20%
Average daily borrowings	17,400,000	6,400,000	439,600,000	273,600,000
Weighted average interest rates on average daily borrowings (in hundredths)	1.20%	1.30%	0.40%	0.20%
Revolving credit facility description						On January 17, 2012, the 2010 Credit Facility was amended and restated ("2012 Credit Facility"). The principal amount was amended to $900 million from the original principal amount of $1.0 billion. Also, the amendment increased the accordion feature from $250 million to $350 million. In addition, the maturity date of the 2010 Credit Facility was extended from December 9, 2013 to January 17, 2017. There were no other significant changes in terms and conditions included in this amendment.	The 2012 Credit Facility is available for AllianceBernstein's and SCB LLC's business purposes, including the support of AllianceBernstein's $1.0 billion commercial paper program. Both AllianceBernstein and SCB LLC can draw directly under the 2012 Credit Facility and management expects to draw on the 2012 Credit Facility from time to time. AllianceBernstein has agreed to guarantee the obligations of SCB LLC under the 2012 Credit Facility. The 2012 Credit Facility contains affirmative, negative and financial covenants, which are customary for facilities of this type, including, among other things, restrictions on dispositions of assets, restrictions on liens, a minimum interest coverage ratio and a maximum leverage ratio. We are in compliance with these covenants. The 2012 Credit Facility also includes customary events of default (with customary grace periods, as applicable), including provisions under which, upon the occurrence of an event of default, all outstanding loans may be accelerated and/or lender's commitments may be terminated. Also, under such provisions, upon the occurrence of certain insolvency or bankruptcy related events of default, all amounts payable under the 2012 Credit Facility would automatically become immediately due and payable, and the lender's commitments would automatically terminate. Amounts under the 2012 Credit Facility may be borrowed, repaid and re-borrowed by us from time to time until the maturity of the facility. Voluntary prepayments and commitment reductions requested by us are permitted at any time without fee (other than customary breakage costs relating to the prepayment of any drawn loans) upon proper notice and subject to a minimum dollar requirement. Borrowings under the 2012 Credit Facility bear interest at a rate per annum, which will be, at our option, a rate equal to an applicable margin, which is subject to adjustment based on the credit ratings of AllianceBernstein, plus one of the following indexes: London Interbank Offered Rate; a floating base rate; or the Federal Funds rate.		In addition, SCB LLC has five uncommitted lines of credit with four financial institutions. Two of these lines of credit permit us to borrow up to an aggregate of approximately $200.0 million while three lines have no stated limit.
Credit facility original principal					1,000,000,000	900,000,000					100,000,000
Credit Facility - Incremental increases in principal					250,000,000	350,000,000		250,000,000	200,000,000
Amount outstanding for one day during period								40,000,000		5,000,000
Interest rate (in hundredths)								1.30%		1.40%
Line of credit facility average borrowings								$ 100,000
Uncommitted lines of credit with financial institutions									5
Financial institutions with uncommitted lines of credit									4
Lines of credit with aggregate borrowing capacity									2
Lines of credit with no stated limit									3