Consolidated Sponsored Investment Funds (Consolidated Sponsored Investment Funds Included In Condensed Consolidated Statements Of Financial Condition) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Valuation and Qualifying Accounts Disclosure [Line Items]
Cash and cash equivalents	$ 4,223	$ 3,506	$ 2,983	$ 3,367
Trading investments	124	267
Other investments	1,445	1,207
Other assets	670	452
Other liabilities	849	721
Consolidated Sponsored Investment Funds [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Cash and cash equivalents	46	196
Trading investments	67	214
Other investments	436	373
Other assets	5	5
Other liabilities	(36)	(37)
Non-controlling interests	(198)	(276)
BlackRock's net interests in consolidated sponsored investment funds	$ 320	$ 475