Short-Term and Long-Term Debt - Short-Term Debt (Details) - Fannie Mae - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Short-Term Debt [Line Items]
Short-term debt, outstanding	$ 19,922	$ 11,188
Short-term debt, weighted-average interest rate (percent)	4.16%	4.33%

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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