Mortgage Loans - Aging (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Recorded investment	$ 3,907,047	$ 3,662,711
Loans 90 Days or More Delinquent and Accruing Interest	37,273	77,196
Nonaccrual Loans with No Allowance	6,532	7,455
30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	23,188	29,473
60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	5,594	10,570
Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	55,897	103,172
Total Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	84,679	143,215
Current
Financing Receivable, Past Due [Line Items]
Recorded investment	3,822,368	3,519,496
Single-family
Financing Receivable, Past Due [Line Items]
Recorded investment	3,505,806	3,285,285
Loans 90 Days or More Delinquent and Accruing Interest	37,151	76,586
Nonaccrual Loans with No Allowance	$ 6,406	$ 7,153
Single-family | Minimum
Table Footnote [Abstract]
Serious delinquency, days past due	90 days	90 days
Single-family | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	$ 22,820	$ 28,333
Single-family | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	5,594	10,570
Single-family | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	54,241	99,484
Single-family | Total Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	82,655	138,387
Single-family | Current
Financing Receivable, Past Due [Line Items]
Recorded investment	3,423,151	3,146,898
Single-family | 20- and 30-year or more, amortizing fixed-rate
Financing Receivable, Past Due [Line Items]
Recorded investment	2,912,188	2,742,203
Loans 90 Days or More Delinquent and Accruing Interest	33,274	68,526
Nonaccrual Loans with No Allowance	5,608	6,028
Single-family | 20- and 30-year or more, amortizing fixed-rate | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	19,980	24,928
Single-family | 20- and 30-year or more, amortizing fixed-rate | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	5,013	9,414
Single-family | 20- and 30-year or more, amortizing fixed-rate | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	48,802	88,276
Single-family | 20- and 30-year or more, amortizing fixed-rate | Total Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	73,795	122,618
Single-family | 20- and 30-year or more, amortizing fixed-rate | Current
Financing Receivable, Past Due [Line Items]
Recorded investment	2,838,393	2,619,585
Single-family | 15-year or less, amortizing fixed-rate
Financing Receivable, Past Due [Line Items]
Recorded investment	524,012	457,059
Loans 90 Days or More Delinquent and Accruing Interest	2,083	4,292
Nonaccrual Loans with No Allowance	185	240
Single-family | 15-year or less, amortizing fixed-rate | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	1,960	1,987
Single-family | 15-year or less, amortizing fixed-rate | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	337	601
Single-family | 15-year or less, amortizing fixed-rate | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	2,477	5,028
Single-family | 15-year or less, amortizing fixed-rate | Total Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	4,774	7,616
Single-family | 15-year or less, amortizing fixed-rate | Current
Financing Receivable, Past Due [Line Items]
Recorded investment	519,238	449,443
Single-family | Adjustable-rate
Financing Receivable, Past Due [Line Items]
Recorded investment	26,969	31,441
Loans 90 Days or More Delinquent and Accruing Interest	434	907
Nonaccrual Loans with No Allowance	72	114
Single-family | Adjustable-rate | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	165	268
Single-family | Adjustable-rate | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	32	97
Single-family | Adjustable-rate | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	537	1,143
Single-family | Adjustable-rate | Total Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	734	1,508
Single-family | Adjustable-rate | Current
Financing Receivable, Past Due [Line Items]
Recorded investment	26,235	29,933
Single-family | Other
Financing Receivable, Past Due [Line Items]
Recorded investment	42,637	54,582
Loans 90 Days or More Delinquent and Accruing Interest	1,360	2,861
Nonaccrual Loans with No Allowance	541	771
Single-family | Other | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	715	1,150
Single-family | Other | 60 - 89 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	212	458
Single-family | Other | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	2,425	5,037
Single-family | Other | Total Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	3,352	6,645
Single-family | Other | Current
Financing Receivable, Past Due [Line Items]
Recorded investment	39,285	47,937
Multifamily
Financing Receivable, Past Due [Line Items]
Recorded investment	401,241	377,426
Loans 90 Days or More Delinquent and Accruing Interest	122	610
Nonaccrual Loans with No Allowance	$ 126	302
Multifamily | Minimum
Table Footnote [Abstract]
Serious delinquency, days past due	60 days
Multifamily | 30 - 59 Days Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	$ 368	1,140
Multifamily | Seriously Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	1,656	3,688
Multifamily | Total Delinquent
Financing Receivable, Past Due [Line Items]
Recorded investment	2,024	4,828
Multifamily | Current
Financing Receivable, Past Due [Line Items]
Recorded investment	$ 399,217	$ 372,598