Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share ("EPS") ) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Earnings Per Share [Line Items]
Net income attributable to BlackRock	$ 642		$ 595		$ 1,768		$ 1,782
Weighted-average shares outstanding	172,359,141		179,034,837		176,116,975		186,187,318
Earnings per basic share attributable to BlackRock common stockholders	$ 3.72		$ 3.28		$ 10.02		$ 9.46
Total diluted weighted-average shares outstanding	175,450,532		181,825,329		178,956,699		188,792,952
Earnings per dilutive share attributable to BlackRock common stockholders	$ 3.65		$ 3.23		$ 9.87		$ 9.33
Unvested RSUs included in participating securities that contain nonforfeitable rights to dividends	200,000		2,200,000		200,000		2,300,000
Earnings Per Share, Diluted [Member]
Earnings Per Share [Line Items]
Net income attributable to common shares	641		588		1,766		1,761
Weighted-average shares outstanding	172,359,141		179,034,837		176,116,975		186,187,318
Dilutive effect of: Non-participating RSUs	2,944,239		2,225,498		2,573,971		1,812,687
Stock options	147,152		564,994		265,753		741,587
Convertible debt							51,360
Total diluted weighted-average shares outstanding	175,450,532		181,825,329		178,956,699		188,792,952
Earnings per dilutive share attributable to BlackRock common stockholders	$ 3.65		$ 3.23		$ 9.87		$ 9.33
Earnings Per Share, Basic [Member]
Earnings Per Share [Line Items]
Net income attributable to BlackRock	642		595		1,768		1,782
Less: Dividends distributed to common shares	259		246		803		760
Dividends distributed to participating RSUs			3		1		9
Undistributed net income attributable to BlackRock	383		346		964		1,013
Percentage of undistributed net income allocated to common shares	99.90%	[1]	98.80%	[1]	99.90%	[1]	98.80%	[1]
Undistributed net income allocated to common shares	382		342		963		1,001
Net income attributable to common shares	$ 641		$ 588		$ 1,766		$ 1,761
Weighted-average shares outstanding	172,359,141		179,034,837		176,116,975		186,187,318
Earnings per basic share attributable to BlackRock common stockholders	$ 3.72		$ 3.28		$ 10.02		$ 9.46

[1] Allocation to common stockholders is based on the total of common and participating security stockholders (which represent unvested RSUs that contain nonforfeitable rights to dividends). For the three months ended September 30, 2012 and 2011, average outstanding participating securities were 0.2 million and 2.2 million, respectively. For the nine months ended September 30, 2012 and 2011, average outstanding participating securities were 0.2 million and 2.3 million, respectively.