Variable Interest Entities Reflects adoption of ASU 2015-12 - Additional Information (Detail) - USD ($) $ in Billions	Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity, Not Primary Beneficiary [Member] \| Sponsored Investment Products [Member]
Variable Interest Entity [Line Items]
Net assets of investments funds	$ 16	$ 12

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_VariableInterestEntityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration