Mortgage Loans - Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total mortgage loans	$ 3,851,488	$ 3,659,247
Single-family
Financing Receivable, Credit Quality Indicator [Line Items]
2021	657,211	1,253,449
2020	1,229,217	367,647
2019	267,707	178,798
2018	129,544	226,092
2017	169,689	272,831
Prior	995,515	972,993
Total mortgage loans	3,448,883	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	533,366	978,509
2020	1,078,503	277,248
2019	254,543	154,357
2018	126,497	220,388
2017	168,392	270,966
Prior	989,190	960,696
Total mortgage loans	3,150,491	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	71,699	163,839
2020	143,550	86,192
2019	12,315	23,574
2018	2,609	5,346
2017	1,160	1,635
Prior	3,939	7,288
Total mortgage loans	235,272	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	52,144	111,073
2020	7,153	4,200
2019	840	832
2018	418	270
2017	93	137
Prior	1,194	2,608
Total mortgage loans	61,842	119,120
Single-family | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2	28
2020	11	7
2019	9	35
2018	20	88
2017	44	93
Prior	1,192	2,401
Total mortgage loans	1,278	2,652
Single-family | 20- and 30-year or more, amortizing fixed-rate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	541,034	1,061,427
2020	1,044,750	323,414
2019	234,251	160,137
2018	115,453	188,912
2017	140,295	222,969
Prior	801,155	785,344
Total mortgage loans	2,876,938	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	420,585	794,156
2020	896,208	233,994
2019	221,164	135,849
2018	112,444	183,315
2017	139,038	221,172
Prior	795,999	775,636
Total mortgage loans	2,585,438	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	69,029	157,500
2020	141,426	85,227
2019	12,239	23,440
2018	2,578	5,270
2017	1,133	1,592
Prior	3,351	5,958
Total mortgage loans	229,756	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	51,418	109,743
2020	7,105	4,186
2019	839	820
2018	414	250
2017	85	124
Prior	912	1,994
Total mortgage loans	60,773	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	2	28
2020	11	7
2019	9	28
2018	17	77
2017	39	81
Prior	893	1,756
Total mortgage loans	971	1,977
Single-family | 15-year or less, amortizing fixed-rate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	114,099	188,797
2020	181,760	42,194
2019	31,983	15,809
2018	12,081	31,518
2017	25,248	46,102
Prior	146,598	132,639
Total mortgage loans	511,769	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	110,924	181,418
2020	179,693	41,374
2019	31,926	15,768
2018	12,068	31,497
2017	25,239	46,088
Prior	146,570	132,596
Total mortgage loans	506,420	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	2,522	6,105
2020	2,020	811
2019	56	35
2018	11	14
2017	5	8
Prior	13	20
Total mortgage loans	4,627	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	653	1,274
2020	47	9
2019	1	3
2018	1	4
2017	2	3
Prior	6	10
Total mortgage loans	710	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	2	3
Prior	9	13
Total mortgage loans	12	22
Single-family | Adjustable-rate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2,078	3,225
2020	2,707	1,994
2019	1,434	2,492
2018	1,692	4,784
2017	3,382	2,683
Prior	15,138	16,263
Total mortgage loans	26,431	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	1,857	2,935
2020	2,602	1,839
2019	1,416	2,412
2018	1,680	4,765
2017	3,376	2,678
Prior	15,131	16,248
Total mortgage loans	26,062	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	148	234
2020	104	152
2019	18	79
2018	12	19
2017	6	5
Prior	6	12
Total mortgage loans	294	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	73	56
2020	1	3
2019	0	1
2018	0	0
2017	0	0
Prior	1	2
Total mortgage loans	75	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	39	360
2018	318	878
2017	764	1,077
Prior	32,624	38,747
Total mortgage loans	33,745	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	37	328
2018	305	811
2017	739	1,028
Prior	31,490	36,216
Total mortgage loans	32,571	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	2	20
2018	8	43
2017	16	30
Prior	569	1,298
Total mortgage loans	595	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	0	8
2018	3	16
2017	6	10
Prior	275	602
Total mortgage loans	284	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	3	9
Prior	290	631
Total mortgage loans	295	652
Single-family | U.S Government
Financing Receivable, Credit Quality Indicator [Line Items]
Total mortgage loans	$ 12,200	$ 13,500