Variable Interest Entities Reflects adoption of ASU 2015-12 - Balances Relating to Variable Interest Entities in which BlackRock is Not Primary Beneficiary (Detail) - Variable Interest Entity, Not Primary Beneficiary [Member] - USD ($) $ in Millions |
Sep. 30, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | $ 3,139 | $ 2,443 |
| Location, Statement of Financial Position, Balance [Axis]: us-gaap:Investments | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | 2,999 | 2,325 |
| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherLiabilities | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | (12) | (12) |
| Location, Statement of Financial Position, Balance [Axis]: us-gaap:SeparateAccountAssets | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | $ 123 | $ 101 |