Debt - Other Debt (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Long-term Debt [Abstract]
Debt instrument recorded at fair value	$ 3,214	$ 3,938
Held by Freddie Mac
Short-term Debt [Abstract]
Other short-term debt par value	112,440	111,080
Other short-term debt carrying amount	$ 112,300	$ 110,877
Other short-term debt weighted average effective rate	1.45%	1.89%
Long-term Debt [Abstract]
Other long-term debt par value	$ 189,818	$ 171,877
Other long-term debt carrying amount	$ 188,135	$ 170,296
Other long-term debt weighted average effective rate	2.30%	2.61%
Total par value	$ 302,258	$ 282,957
Total other debt	300,435	281,173
Debt instrument recorded at fair value	3,000	3,700
Balance Net Of Callable Other Long Term Debt	84,800	95,100
Held by Freddie Mac | Other long-term debt | Other long-term debt - 2020
Long-term Debt [Abstract]
Other long-term debt par value	32,507	45,133
Other long-term debt carrying amount	$ 32,505	$ 45,127
Other long-term debt weighted average effective rate	1.81%	1.76%
Held by Freddie Mac | Other long-term debt | Other long-term debt - 2021
Long-term Debt [Abstract]
Other long-term debt par value	$ 45,202	$ 30,069
Other long-term debt carrying amount	$ 45,198	$ 30,072
Other long-term debt weighted average effective rate	1.23%	1.89%
Held by Freddie Mac | Other long-term debt | Other long-term debt - 2022
Long-term Debt [Abstract]
Other long-term debt par value	$ 25,236	$ 23,185
Other long-term debt carrying amount	$ 25,219	$ 23,166
Other long-term debt weighted average effective rate	1.94%	2.20%
Held by Freddie Mac | Other long-term debt | Other long-term debt - 2023
Long-term Debt [Abstract]
Other long-term debt par value	$ 17,680	$ 13,413
Other long-term debt carrying amount	$ 17,661	$ 13,393
Other long-term debt weighted average effective rate	1.98%	2.22%
Held by Freddie Mac | Other long-term debt | Other long-term debt - 2024
Long-term Debt [Abstract]
Other long-term debt par value	$ 22,975	$ 26,966
Other long-term debt carrying amount	$ 22,938	$ 26,924
Other long-term debt weighted average effective rate	2.13%	2.22%
Held by Freddie Mac | Other long-term debt | Other long-term debt - Thereafter
Long-term Debt [Abstract]
Other long-term debt par value	$ 31,564	$ 17,615
Other long-term debt carrying amount	$ 29,270	$ 15,294
Other long-term debt weighted average effective rate	3.49%	5.13%
Held by Freddie Mac | STACR and SCR debt
Long-term Debt [Abstract]
Other long-term debt par value	$ 14,654	$ 15,496
Other long-term debt carrying amount	$ 14,271	$ 15,652
Other long-term debt weighted average effective rate	5.66%	5.64%
Held by Freddie Mac | Hedging-Related Basis Adjustments
Long-term Debt [Abstract]
Other long-term debt carrying amount	$ 1,073	$ 668
Held by Freddie Mac | Discount notes and Reference Bills
Short-term Debt [Abstract]
Other short-term debt par value	57,822	60,830
Other short-term debt carrying amount	$ 57,685	$ 60,629
Other short-term debt weighted average effective rate	1.33%	1.67%
Held by Freddie Mac | Medium-term notes
Short-term Debt [Abstract]
Other short-term debt par value	$ 40,313	$ 40,407
Other short-term debt carrying amount	$ 40,310	$ 40,405
Other short-term debt weighted average effective rate	2.07%	2.31%
Held by Freddie Mac | Securities Sold under Agreements to Repurchase
Short-term Debt [Abstract]
Other short-term debt par value	$ 14,305	$ 9,843
Other short-term debt carrying amount	$ 14,305	$ 9,843
Other short-term debt weighted average effective rate	0.16%	1.46%