Total Equity and Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss) Components) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Jun. 30, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Dec. 31, 2010
Total Equity And Other Comprehensive Income [Abstract]
Net unrealized gains on non-OTTI securities, pretax	$ 1,960				$ 1,098
Net unrealized gains on non-OTTI securities, after-tax	1,242		946		696		664		419		95
Net unrealized gains (losses) on OTTI securities, pretax	(304)				(1,166)
OTTI losses on debt securities, after-tax	(192)		(476)		(738)		(617)		(520)		(646)
Net unrealized gains on cash flow hedge derivatives, pretax	1,024				1,131
Net unrealized gains on cash flow hedge derivatives, after-tax	656		664		717		731		544		522
Pension and other postretirement benefit plan adjustments, pretax	(1,082)				(1,191)
Pension and other postretirement benefit plan adjustments, after-tax	(686)		(700)		(755)		(370)		(373)		(380)
Other, net pretax	(56)				(51)
Other ,net After-tax	(29)	[1]	(32)	[1]	(25)	[1]	(11)	[1]	(1)	[1]	(22)	[1]
Accumulated other comprehensive income (loss), pretax	1,542				(179)
Accumulated other comprehensive income (loss), after-tax	$ 991				$ (105)

[1] Consists of foreign currency translation adjustments and deferred tax adjustments on BlackRock's other comprehensive income in 2012.