Variable Interest Entities (Narrative) (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Y	Sep. 30, 2011	Dec. 31, 2011 Y
Variable Interest Entity [Line Items]
Net gain (loss) attributable to nonredeemable non-controlling interests	$ 10,000,000	$ (25,000,000)	$ 15,000,000	$ (26,000,000)
Weighted-average maturities of bank loans and bonds, years			4.2		4.2
Other sponsored investments funds collective trusts	1,200,000,000,000		1,200,000,000,000		1,000,000,000,000
Credit protection			17,000,000		17,000,000
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Net gain (loss) attributable to nonredeemable non-controlling interests	2,000,000	(16,000,000)	1,000,000	(36,000,000)
Non-operating (loss)	2,000,000	(16,000,000)	1,000,000	(36,000,000)
Minimum [Member]
Variable Interest Entity [Line Items]
Other sponsored investments funds	1,400,000,000,000		1,400,000,000,000		1,200,000,000,000
Maximum [Member]
Variable Interest Entity [Line Items]
Other sponsored investments funds	$ 1,500,000,000,000		$ 1,500,000,000,000		$ 1,300,000,000,000