Variable Interest Entities (Balances Relating To Variable Interest Entities In Which BlackRock Is Not The Primary Beneficiary) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Variable Interest Entity [Line Items]
Collective trusts	$ 1,200,000	$ 1,000,000
Investments [Member]
Variable Interest Entity [Line Items]
CDOs/CLOs	1	1
Other	17	18
Total	18	19
Advisory Fee Receivables [Member]
Variable Interest Entity [Line Items]
CDOs/CLOs	3	2
Collective trusts	186	184
Other	63	54
Total	252	240
Other Net Assets (Liabilities) [Member]
Variable Interest Entity [Line Items]
CDOs/CLOs	(4)	(3)
Other		(5)
Total	(4)	(8)
Maximum Risk Of Loss [Member]
Variable Interest Entity [Line Items]
CDOs/CLOs	21	20
Collective trusts	186	184
Other	80	72
Total	$ 287	$ 276