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 ($) |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Investments [Member] | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | $ 342,000,000 | $ 263,000,000 |
| Advisory Fee Receivables [Member] | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | 30,000,000 | 15,000,000 |
| Other Net Assets (Liabilities) [Member] | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | (7,000,000) | (7,000,000) |
| Maximum Risk of Loss [Member] | ||
| Variable Interest Entity [Line Items] | ||
| Sponsored investment products | $ 389,000,000 | $ 295,000,000 |