Debt - Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Debt instrument recorded at fair value	$ 5,697	$ 2,339
Held by Freddie Mac
Debt Instrument [Line Items]
Par Value Of Long Term Debt	168,923	172,943
Long-term Debt	$ 165,354	$ 167,333
Long-term debt weighted average effective rate	3.97%	3.65%
Debt instrument recorded at fair value	$ 200	$ 300
Fixed Rate \| Held by Freddie Mac
Debt Instrument [Line Items]
Par Value Of Long Term Debt	102,819	130,965
Long-term Debt	$ 100,558	$ 126,815
Long-term debt weighted average effective rate	3.32%	3.09%
Fixed Rate \| Held by Freddie Mac \| Callable Medium Term Notes
Debt Instrument [Line Items]
Par Value Of Long Term Debt	$ 95,000	$ 112,600
Variable Rate \| Held by Freddie Mac
Debt Instrument [Line Items]
Par Value Of Long Term Debt	60,620	35,906
Long-term Debt	$ 60,610	$ 35,893
Long-term debt weighted average effective rate	4.86%	5.16%
Variable Rate \| Held by Freddie Mac \| Callable Medium Term Notes
Debt Instrument [Line Items]
Par Value Of Long Term Debt	$ 800	$ 1,300
Zero Coupon \| Held by Freddie Mac
Debt Instrument [Line Items]
Par Value Of Long Term Debt	4,748	4,748
Long-term Debt	$ 3,406	$ 3,254
Long-term debt weighted average effective rate	6.27%	6.22%
Other \| Held by Freddie Mac
Debt Instrument [Line Items]
Par Value Of Long Term Debt	$ 736	$ 1,324
Long-term Debt	$ 780	$ 1,371
Long-term debt weighted average effective rate	10.22%	10.90%