S000003863 [Member] Investment Objectives and Goals - BlackRock Balanced Portfolio |
Dec. 31, 2025 |
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| Prospectus [Line Items] | |
| Risk/Return [Heading] | Fund Overview Key Facts About BlackRock Balanced Portfolio |
| Objective [Heading] | Investment Objective |
| Objective, Primary [Text Block] | The investment objective of BlackRock Balanced Portfolio (the “Balanced Portfolio” or the “Fund”) (formerly known as BlackRock Sustainable Balanced Portfolio), a series of BlackRock Series Fund, Inc. (the “Corporation”), is to seek high total investment return.
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