Mortgage Loans - Aging (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	$ 4,152,651	$ 4,149,258
Loans 90 Days or More Delinquent and Accruing Interest	537	1,775
Nonaccrual Loans with No Allowance	$ 4,976	4,476
Table Footnote [Abstract]
Serious delinquency, days past due	90 days
Total Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	$ 65,352	66,479
30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	35,560	36,184
60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	9,026	8,625
Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	20,766	21,670
Current
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	4,087,299	4,082,779
Single-family
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	3,676,082	3,687,904
Loans 90 Days or More Delinquent and Accruing Interest	452	1,604
Nonaccrual Loans with No Allowance	3,992	3,882
Table Footnote [Abstract]
Mortgage loans in process of foreclosure	$ 4,600	$ 4,600
Single-family | Minimum
Table Footnote [Abstract]
Serious delinquency, days past due	90 days	90 days
Single-family | Total Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	$ 62,732	$ 64,331
Single-family | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	34,956	35,735
Single-family | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	9,026	8,625
Single-family | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	18,750	19,971
Single-family | Current
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	3,613,350	3,623,573
Single-family | 20- and 30-year or more, amortizing fixed-rate
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	3,245,481	3,208,042
Loans 90 Days or More Delinquent and Accruing Interest	401	1,371
Nonaccrual Loans with No Allowance	3,589	3,457
Single-family | 20- and 30-year or more, amortizing fixed-rate | Total Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	58,837	59,871
Single-family | 20- and 30-year or more, amortizing fixed-rate | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	32,625	33,119
Single-family | 20- and 30-year or more, amortizing fixed-rate | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	8,534	8,093
Single-family | 20- and 30-year or more, amortizing fixed-rate | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	17,678	18,659
Single-family | 20- and 30-year or more, amortizing fixed-rate | Current
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	3,186,644	3,148,171
Single-family | 15-year or less, amortizing fixed-rate
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	383,222	428,413
Loans 90 Days or More Delinquent and Accruing Interest	24	74
Nonaccrual Loans with No Allowance	196	176
Single-family | 15-year or less, amortizing fixed-rate | Total Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	2,518	2,815
Single-family | 15-year or less, amortizing fixed-rate | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	1,636	1,846
Single-family | 15-year or less, amortizing fixed-rate | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	316	319
Single-family | 15-year or less, amortizing fixed-rate | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	566	650
Single-family | 15-year or less, amortizing fixed-rate | Current
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	380,704	425,598
Single-family | Adjustable-rate
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	25,732	26,358
Loans 90 Days or More Delinquent and Accruing Interest	3	11
Nonaccrual Loans with No Allowance	20	21
Single-family | Adjustable-rate | Total Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	286	326
Single-family | Adjustable-rate | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	165	184
Single-family | Adjustable-rate | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	32	42
Single-family | Adjustable-rate | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	89	100
Single-family | Adjustable-rate | Current
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	25,446	26,032
Single-family | Other
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	21,647	25,091
Loans 90 Days or More Delinquent and Accruing Interest	24	148
Nonaccrual Loans with No Allowance	187	228
Single-family | Other | Total Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	1,091	1,319
Single-family | Other | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	530	586
Single-family | Other | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	144	171
Single-family | Other | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	417	562
Single-family | Other | Current
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	20,556	23,772
Multifamily
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	476,569	461,354
Loans 90 Days or More Delinquent and Accruing Interest	85	171
Nonaccrual Loans with No Allowance	$ 984	594
Multifamily | Minimum
Table Footnote [Abstract]
Serious delinquency, days past due	60 days
Multifamily | Maximum
Table Footnote [Abstract]
Serious delinquency, days past due	89 days
Multifamily | Total Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	$ 2,620	2,148
Multifamily | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	604	449
Multifamily | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	2,016	1,699
Multifamily | Current
Financing Receivable, Past Due [Line Items]
Loans held for investment, excluding fair value option	$ 473,949	$ 459,206