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 ($) |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Investments [Member] | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | $ 539,000,000 | $ 348,000,000 |
| Advisory Fee Receivables [Member] | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | 71,000,000 | 43,000,000 |
| Other Net Assets (Liabilities) [Member] | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | (10,000,000) | (6,000,000) |
| Maximum Risk of Loss [Member] | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | $ 627,000,000 | $ 408,000,000 |