Total Equity and Other Comprehensive Income (Change in Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Total Equity And Other Comprehensive Income [Abstract]
Net unrealized gains on non-OTTI securities beginning balance, after-tax	$ 946		$ 419		$ 696		$ 95
Increase in net unrealized gains losses for non-OTTI securities, Pretax	506		436		1,027		1,098
Increase in net unrealized gains losses for non-OTTI securities, Tax	(184)		(149)		(376)		(388)
Increase in net unrealized gains losses for non-OTTI securities, After-tax	322		287		651		710
Less: net gains realized in net income, pretax	40		68		165		221
Less: net gains realized in net income, tax	(14)		(26)		(60)		(80)
Less: net gains realized in net income, Net of Tax, Total	26		42		105		141
Net unrealized gains on non-OTTI securities	466		368		862		877
Net unrealized gains on non-OTTI securities, Tax	(170)		(123)		(316)		(308)
Net unrealized gains on non-OTTI securities, After-tax	296		245		546		569
Net unrealized gains on non-OTTI securities ending balance, after-tax	1,242		664		1,242		664
Net unrealized gains (losses) on OTTI securities, After-tax, Beginning Balance	(476)		(520)		(738)		(646)
Net increase in OTTI losses on debt securities, pretax	424		(156)		760		(76)
Net increase in OTTI losses on debt securities, Tax	(156)		38		(279)		15
Net increase in OTTI losses on debt securities, After-tax	268		(118)		481		(61)
Less: Net losses realized on sale of securities, Pretax			0		(6)		(34)
Less: Net losses realized on sale of securities, Tax			0		2		12
Less: Net losses realized on sale of securities After-tax			0		(4)		(22)
Less: Net OTTI losses realized in net income	(24)		(35)		(96)		(108)
Less: Net OTTI losses realized in net income, Tax	8		14		35		40
Less: Net OTTI losses realized in net income, After-tax	(16)		(21)		(61)		(68)
Net unrealized gains (losses) on OTTI securities, Pretax	448		(121)		862		66
Net unrealized gains (losses) on OTTI securities, Tax	(164)		24		(316)		(37)
Net unrealized gains (losses) on OTTI securities, After-tax	284		(97)		546		29
Net unrealized gains (losses) on OTTI securities, After-tax, Ending Balance	(192)		(617)		(192)		(617)
Net unrealized gains (losses) on cash flow hedge derivatives, Beginning Balance, After-tax	664		544		717		522
Increase in net unrealized gains on cash flow hedge derivatives, Pretax	103		423		310		703
Increase in net unrealized gains on cash flow hedge derivatives, Tax	(57)		(155)		(133)		(258)
Increase in net unrealized gains on cash flow hedge derivatives, After-tax	46		268		177		445
Less: net gains realized in net income on derivatives, pretax	126		128		417		373
Less: net gains realized in net income on derivatives, tax	(72)		(47)		(179)		(137)
Less: net gains realized in net income on derivatives, Net of Tax, Total	54		81		238		236
Net unrealized gains (losses) on cash flow hedge derivatives, pretax	(23)		295		(107)		330
Net unrealized gains (losses) on cash flow hedge derivatives, tax	15		(108)		46		(121)
Net unrealized gains (losses) on cash flow hedge derivatives, Net of tax, Total	(8)		187		(61)		209
Net unrealized gains (losses) on cash flow hedge derivatives, Ending Balance, After-tax	656		731		656		731
Pension and other postretirement benefit plan adjustments, after-tax, beginning balance	(700)		(373)		(755)		(380)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	22		3		109		14
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax	(8)				(40)		(4)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax, Total	14		3		69		10
Pension and other postretirement benefit plan adjustments, after-tax, ending balance	(686)		(370)		(686)		(370)
Other Accumulated Other Comprehensive Income Balance, beginning balance	(32)	[1]	(1)	[1]	(25)	[1]	(22)	[1]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax	13	[1]	(12)	[1]	(5)	[1]	27	[1]
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	(5)		1	[1]	2	[1]	(9)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Total	8	[1]	(11)	[1]	(3)	[1]	18	[1]
BlackRock deferred tax adjustment, Tax	(5)		1	[1]	(1)	[1]	(7)	[1]
BlackRock deferred tax adjustment, After-tax	(5)	[1]	1		(1)	[1]	(7)	[1]
Other	13	[1]	(12)	[1]	(5)	[1]	27	[1]
Change in other, net Tax	(10)		2		1	[1]	(16)	[1]
Change in other, net After-tax	3	[1]	(10)	[1]	(4)	[1]	11	[1]
Other Accumulated Other Comprehensive Income Balance, ending balance	$ (29)	[1]	$ (11)	[1]	$ (29)	[1]	$ (11)	[1]

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