Mortgage Loans - Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total mortgage loans	$ 3,902,514	$ 3,659,247
Single-family
Financing Receivable, Credit Quality Indicator [Line Items]
2021	941,976	1,253,449
2020	1,149,674	367,647
2019	233,953	178,798
2018	113,059	226,092
2017	150,802	272,831
Prior	904,706	972,993
Total mortgage loans	3,494,170	3,271,810
Single-family | Estimated mark-to-market loan-to-value ratio less than or equal to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	775,494	978,509
2020	1,083,114	277,248
2019	229,468	154,357
2018	111,475	220,388
2017	149,964	270,966
Prior	900,512	960,696
Total mortgage loans	3,250,027	2,862,164
Single-family | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	110,368	163,839
2020	63,902	86,192
2019	3,851	23,574
2018	1,265	5,346
2017	745	1,635
Prior	2,625	7,288
Total mortgage loans	182,756	287,874
Single-family | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	56,111	111,073
2020	2,652	4,200
2019	627	832
2018	304	270
2017	63	137
Prior	774	2,608
Total mortgage loans	60,531	119,120
Single-family | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	3	28
2020	6	7
2019	7	35
2018	15	88
2017	30	93
Prior	795	2,401
Total mortgage loans	856	2,652
Single-family | 20- and 30-year or more, amortizing fixed-rate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	775,818	1,061,427
2020	978,931	323,414
2019	204,337	160,137
2018	100,616	188,912
2017	124,399	222,969
Prior	728,087	785,344
Total mortgage loans	2,912,188	2,742,203
Single-family | 20- and 30-year or more, amortizing fixed-rate | Estimated mark-to-market loan-to-value ratio less than or equal to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	613,085	794,156
2020	912,984	233,994
2019	199,883	135,849
2018	99,052	183,315
2017	123,581	221,172
Prior	724,677	775,636
Total mortgage loans	2,673,262	2,344,122
Single-family | 20- and 30-year or more, amortizing fixed-rate | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	107,349	157,500
2020	63,299	85,227
2019	3,821	23,440
2018	1,250	5,270
2017	731	1,592
Prior	2,226	5,958
Total mortgage loans	178,676	278,987
Single-family | 20- and 30-year or more, amortizing fixed-rate | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	55,381	109,743
2020	2,642	4,186
2019	626	820
2018	302	250
2017	60	124
Prior	585	1,994
Total mortgage loans	59,596	117,117
Single-family | 20- and 30-year or more, amortizing fixed-rate | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	3	28
2020	6	7
2019	7	28
2018	12	77
2017	27	81
Prior	599	1,756
Total mortgage loans	654	1,977
Single-family | 15-year or less, amortizing fixed-rate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	160,849	188,797
2020	168,279	42,194
2019	28,334	15,809
2018	10,719	31,518
2017	22,811	46,102
Prior	133,020	132,639
Total mortgage loans	524,012	457,059
Single-family | 15-year or less, amortizing fixed-rate | Estimated mark-to-market loan-to-value ratio less than or equal to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	157,618	181,418
2020	167,706	41,374
2019	28,311	15,768
2018	10,712	31,497
2017	22,806	46,088
Prior	133,000	132,596
Total mortgage loans	520,153	448,741
Single-family | 15-year or less, amortizing fixed-rate | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2,642	6,105
2020	564	811
2019	23	35
2018	5	14
2017	3	8
Prior	9	20
Total mortgage loans	3,246	6,993
Single-family | 15-year or less, amortizing fixed-rate | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	589	1,274
2020	9	9
2019	0	3
2018	1	4
2017	1	3
Prior	4	10
Total mortgage loans	604	1,303
Single-family | 15-year or less, amortizing fixed-rate | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	3
2018	1	3
2017	1	3
Prior	7	13
Total mortgage loans	9	22
Single-family | Adjustable-rate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	5,309	3,225
2020	2,464	1,994
2019	1,246	2,492
2018	1,429	4,784
2017	2,882	2,683
Prior	13,639	16,263
Total mortgage loans	26,969	31,441
Single-family | Adjustable-rate | Estimated mark-to-market loan-to-value ratio less than or equal to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	4,791	2,935
2020	2,424	1,839
2019	1,239	2,412
2018	1,424	4,765
2017	2,880	2,678
Prior	13,636	16,248
Total mortgage loans	26,394	30,877
Single-family | Adjustable-rate | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	377	234
2020	39	152
2019	7	79
2018	5	19
2017	2	5
Prior	3	12
Total mortgage loans	433	501
Single-family | Adjustable-rate | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	141	56
2020	1	3
2019	0	1
2018	0	0
2017	0	0
Prior	0	2
Total mortgage loans	142	62
Single-family | Adjustable-rate | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior	0	1
Total mortgage loans	0	1
Single-family | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	45
2019	36	360
2018	295	878
2017	710	1,077
Prior	29,960	38,747
Total mortgage loans	31,001	41,107
Single-family | Other | Estimated mark-to-market loan-to-value ratio less than or equal to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	41
2019	35	328
2018	287	811
2017	697	1,028
Prior	29,199	36,216
Total mortgage loans	30,218	38,424
Single-family | Other | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	2
2019	0	20
2018	5	43
2017	9	30
Prior	387	1,298
Total mortgage loans	401	1,393
Single-family | Other | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	2
2019	1	8
2018	1	16
2017	2	10
Prior	185	602
Total mortgage loans	189	638
Single-family | Other | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	4
2018	2	8
2017	2	9
Prior	189	631
Total mortgage loans	193	652
Single-family | U.S Government
Financing Receivable, Credit Quality Indicator [Line Items]
Total mortgage loans	$ 11,600	$ 13,500