Fair Value - Levels Hierarchy (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Assets:
Total Fair Value	$ 679	$ 696
Mortgage loans held for investment, net of allowance for loan losses	3,599	3,645
Derivative assets at fair value	153	175
Derivative assets, gross amount offset	(164)	(154)
Liabilities:
Derivative liabilities	308	168
Fannie Mae
Liabilities:
Long-term debt:	1,132	1,161
Consolidated Trusts
Liabilities:
Long-term debt:	15,972	16,260
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Trading securities	47,537	46,898
Total Fair Value	0	0
Mortgage loans held for investment, net of allowance for loan losses	0	0
Derivative assets at fair value	0	0
Total financial assets	83,774	79,889
Liabilities:
Derivative liabilities	0	0
Total financial liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fannie Mae
Liabilities:
Long-term debt:	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Consolidated Trusts
Liabilities:
Long-term debt:	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Trading securities	2,841	3,184
Total Fair Value	57	62
Mortgage loans held for investment, net of allowance for loan losses	3,489,281	3,437,979
Derivative assets at fair value	290	300
Total financial assets	3,576,790	3,512,490
Liabilities:
Derivative liabilities	4,153	4,764
Total financial liabilities	3,716,103	3,648,996
Significant Other Observable Inputs (Level 2) \| Fannie Mae
Liabilities:
Long-term debt:	124,585	122,066
Significant Other Observable Inputs (Level 2) \| Consolidated Trusts
Liabilities:
Long-term debt:	3,573,396	3,511,958
Significant Unobservable Inputs (Level 3)
Assets:
Trading securities	32	47
Total Fair Value	622	634
Mortgage loans held for investment, net of allowance for loan losses	170,658	171,857
Derivative assets at fair value	27	29
Total financial assets	172,014	174,762
Liabilities:
Derivative liabilities	65	66
Total financial liabilities	42,200	42,840
Significant Unobservable Inputs (Level 3) \| Fannie Mae
Liabilities:
Long-term debt:	577	558
Significant Unobservable Inputs (Level 3) \| Consolidated Trusts
Liabilities:
Long-term debt:	41,490	42,150
Recurring
Assets:
Trading securities	50,410	50,129
Total Fair Value	679	696
Mortgage loans held for investment, net of allowance for loan losses	3,599	3,645
Derivative assets at fair value	153	175
Derivative assets, gross amount offset	(164)	(154)
Total financial assets	54,841	54,645
Liabilities:
Long-term debt:	17,104	17,421
Derivative liabilities	308	168
Derivative liabilities, gross amount offset	(3,910)	(4,662)
Total financial liabilities	17,412	17,589
Recurring \| Fannie Mae
Liabilities:
Long-term debt:	1,132	1,161
Recurring \| Consolidated Trusts
Liabilities:
Long-term debt:	15,972	16,260
Recurring \| Mortgage-related
Assets:
Trading securities	2,852	3,211
Recurring \| Non-mortgage-related securities
Assets:
Trading securities	47,558	46,918
Recurring \| Other agency
Assets:
Total Fair Value	414	426
Recurring \| Other mortgage-related
Assets:
Total Fair Value	265	270
Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Trading securities	47,537	46,898
Total Fair Value	0	0
Mortgage loans held for investment, net of allowance for loan losses	0	0
Derivative assets at fair value	0	0
Total financial assets	47,537	46,898
Liabilities:
Long-term debt:	0	0
Derivative liabilities	0	0
Total financial liabilities	0	0
Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fannie Mae
Liabilities:
Long-term debt:	0	0
Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Consolidated Trusts
Liabilities:
Long-term debt:	0	0
Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Mortgage-related
Assets:
Trading securities	0	0
Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Non-mortgage-related securities
Assets:
Trading securities	47,537	46,898
Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Other agency
Assets:
Total Fair Value	0	0
Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Other mortgage-related
Assets:
Total Fair Value	0	0
Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Trading securities	2,841	3,184
Total Fair Value	57	62
Mortgage loans held for investment, net of allowance for loan losses	3,073	3,102
Derivative assets at fair value	290	300
Total financial assets	6,261	6,648
Liabilities:
Long-term debt:	16,721	17,043
Derivative liabilities	4,153	4,764
Total financial liabilities	20,874	21,807
Recurring \| Significant Other Observable Inputs (Level 2) \| Fannie Mae
Liabilities:
Long-term debt:	882	919
Recurring \| Significant Other Observable Inputs (Level 2) \| Consolidated Trusts
Liabilities:
Long-term debt:	15,839	16,124
Recurring \| Significant Other Observable Inputs (Level 2) \| Mortgage-related
Assets:
Trading securities	2,820	3,164
Recurring \| Significant Other Observable Inputs (Level 2) \| Non-mortgage-related securities
Assets:
Trading securities	21	20
Recurring \| Significant Other Observable Inputs (Level 2) \| Other agency
Assets:
Total Fair Value	52	55
Recurring \| Significant Other Observable Inputs (Level 2) \| Other mortgage-related
Assets:
Total Fair Value	5	7
Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Trading securities	32	47
Total Fair Value	622	634
Mortgage loans held for investment, net of allowance for loan losses	526	543
Derivative assets at fair value	27	29
Total financial assets	1,207	1,253
Liabilities:
Long-term debt:	383	378
Derivative liabilities	65	66
Total financial liabilities	448	444
Recurring \| Significant Unobservable Inputs (Level 3) \| Fannie Mae
Liabilities:
Long-term debt:	250	242
Recurring \| Significant Unobservable Inputs (Level 3) \| Consolidated Trusts
Liabilities:
Long-term debt:	133	136
Recurring \| Significant Unobservable Inputs (Level 3) \| Mortgage-related
Assets:
Trading securities	32	47
Recurring \| Significant Unobservable Inputs (Level 3) \| Non-mortgage-related securities
Assets:
Trading securities	0	0
Recurring \| Significant Unobservable Inputs (Level 3) \| Other agency
Assets:
Total Fair Value	362	371
Recurring \| Significant Unobservable Inputs (Level 3) \| Other mortgage-related
Assets:
Total Fair Value	$ 260	$ 263

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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