Consolidated Sponsored Investment Funds (Narrative) (Detail) (Consolidated Sponsored Investment Funds [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Consolidated Sponsored Investment Funds [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
BlackRock's total exposure to consolidated sponsored investment funds	$ 320	$ 475

This item represents the entity's ownership percentage in the investee multiplied by the investee's total equity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant