Variable Interest Entities (Balances Relating To Variable Interest Entities In Which BlackRock Is The Primary Beneficiary) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 4,223		$ 3,506	$ 2,983	$ 3,367
Other investments	1,445		1,207
Other liabilities	(849)		(721)
Non-controlling interests of consolidated VIEs	(170)		(184)
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	292		54
Bank loans	1,495		1,459
Bonds	125		145
Other investments	33	[1]	35
Total assets of consolidated VIE	1,683		1,639
Borrowings	(1,843)		(1,574)
Other liabilities	(9)		(9)
Appropriated retained earnings	(56)		(72)
Non-controlling interests of consolidated VIEs	(34)		(38)
Total net interests in consolidated VIEs	$ 13

[1] Amount within Level 3 included $24 million and $2 million of underlying third-party private equity funds and direct investments in private equity companies held by private equity fund, respectively.