Service Shares [Member] Annual Total Returns |
12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
Dec. 31, 2022 |
Dec. 31, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Service Shares | BlackRock National Municipal Fund | Service Shares | ||||||||||
| Prospectus [Line Items] | ||||||||||
| Annual Return [Percent] | 2.99% | 1.62% | 5.97% | (10.44%) | 2.03% | 4.01% | 7.02% | 0.46% | 5.07% | 0.20% |