Class K [Member] Expense Example - Class K - BlackRock National Municipal Fund - Class K Shares	Jun. 30, 2026 USD ($)
Prospectus [Line Items]
Expense Example, with Redemption, 1 Year	$ 46
Expense Example, with Redemption, 3 Years	151
Expense Example, with Redemption, 5 Years	266
Expense Example, with Redemption, 10 Years	$ 601

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