Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	$ 3,745,661	$ 3,662,711
Financing Receivable, before Allowance for Credit Loss	3,741,684	3,659,247
Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	3,353,794	3,285,285
Financing Receivable, Originated in Current Fiscal Year	285,659	1,253,449
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,291,027	367,647
Financing Receivable, Originated Two Years before Latest Fiscal Year	308,023	178,798
Financing Receivable, Originated Three Years before Latest Fiscal Year	151,730	226,092
Financing Receivable, Originated Four Years before Latest Fiscal Year	194,462	272,831
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,110,004	972,993
Financing Receivable, before Allowance for Credit Loss	3,340,905	3,271,810
Single-family [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	28
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	25	7
Financing Receivable, Originated Two Years before Latest Fiscal Year	6	35
Financing Receivable, Originated Three Years before Latest Fiscal Year	29	88
Financing Receivable, Originated Four Years before Latest Fiscal Year	66	93
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,901	2,401
Financing Receivable, before Allowance for Credit Loss	2,027	2,652
Single-family [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	235,160	978,509
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,038,857	277,248
Financing Receivable, Originated Two Years before Latest Fiscal Year	254,428	154,357
Financing Receivable, Originated Three Years before Latest Fiscal Year	140,355	220,388
Financing Receivable, Originated Four Years before Latest Fiscal Year	191,464	270,966
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,099,497	960,696
Financing Receivable, before Allowance for Credit Loss	2,959,761	2,862,164
Single-family [Member] | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	24,978	163,839
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	185,437	86,192
Financing Receivable, Originated Two Years before Latest Fiscal Year	51,871	23,574
Financing Receivable, Originated Three Years before Latest Fiscal Year	10,761	5,346
Financing Receivable, Originated Four Years before Latest Fiscal Year	2,761	1,635
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	6,584	7,288
Financing Receivable, before Allowance for Credit Loss	282,392	287,874
Single-family [Member] | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	25,521	111,073
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	66,708	4,200
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,718	832
Financing Receivable, Originated Three Years before Latest Fiscal Year	585	270
Financing Receivable, Originated Four Years before Latest Fiscal Year	171	137
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	2,022	2,608
Financing Receivable, before Allowance for Credit Loss	96,725	119,120
Single-family [Member] | Government [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss	12,900	13,500
Single-family [Member] | Fixed Rate Residential Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	2,792,740	2,742,203
Financing Receivable, Originated in Current Fiscal Year	236,035	1,061,427
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,095,122	323,414
Financing Receivable, Originated Two Years before Latest Fiscal Year	270,021	160,137
Financing Receivable, Originated Three Years before Latest Fiscal Year	135,546	188,912
Financing Receivable, Originated Four Years before Latest Fiscal Year	161,512	222,969
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	894,504	785,344
Financing Receivable, before Allowance for Credit Loss	2,792,740	2,742,203
Single-family [Member] | Fixed Rate Residential Mortgage | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	28
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	25	7
Financing Receivable, Originated Two Years before Latest Fiscal Year	6	28
Financing Receivable, Originated Three Years before Latest Fiscal Year	24	77
Financing Receivable, Originated Four Years before Latest Fiscal Year	58	81
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,402	1,756
Financing Receivable, before Allowance for Credit Loss	1,515	1,977
Single-family [Member] | Fixed Rate Residential Mortgage | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	187,046	794,156
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	848,710	233,994
Financing Receivable, Originated Two Years before Latest Fiscal Year	216,806	135,849
Financing Receivable, Originated Three Years before Latest Fiscal Year	124,252	183,315
Financing Receivable, Originated Four Years before Latest Fiscal Year	158,591	221,172
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	885,994	775,636
Financing Receivable, before Allowance for Credit Loss	2,421,399	2,344,122
Single-family [Member] | Fixed Rate Residential Mortgage | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	23,830	157,500
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	180,295	85,227
Financing Receivable, Originated Two Years before Latest Fiscal Year	51,499	23,440
Financing Receivable, Originated Three Years before Latest Fiscal Year	10,692	5,270
Financing Receivable, Originated Four Years before Latest Fiscal Year	2,706	1,592
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	5,552	5,958
Financing Receivable, before Allowance for Credit Loss	274,574	278,987
Single-family [Member] | Fixed Rate Residential Mortgage | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	25,159	109,743
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	66,092	4,186
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,710	820
Financing Receivable, Originated Three Years before Latest Fiscal Year	578	250
Financing Receivable, Originated Four Years before Latest Fiscal Year	157	124
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,556	1,994
Financing Receivable, before Allowance for Credit Loss	95,252	117,117
Single-family [Member] | Adjustable Rate Residential Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	27,785	31,441
Financing Receivable, Originated in Current Fiscal Year	128	3,225
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,975	1,994
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,689	2,492
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,041	4,784
Financing Receivable, Originated Four Years before Latest Fiscal Year	3,997	2,683
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	16,955	16,263
Financing Receivable, before Allowance for Credit Loss	27,785	31,441
Single-family [Member] | Adjustable Rate Residential Mortgage [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1	1
Financing Receivable, before Allowance for Credit Loss	1	1
Single-family [Member] | Adjustable Rate Residential Mortgage [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	111	2,935
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,757	1,839
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,608	2,412
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,006	4,765
Financing Receivable, Originated Four Years before Latest Fiscal Year	3,982	2,678
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	16,940	16,248
Financing Receivable, before Allowance for Credit Loss	27,404	30,877
Single-family [Member] | Adjustable Rate Residential Mortgage [Member] | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	11	234
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	189	152
Financing Receivable, Originated Two Years before Latest Fiscal Year	79	79
Financing Receivable, Originated Three Years before Latest Fiscal Year	35	19
Financing Receivable, Originated Four Years before Latest Fiscal Year	15	5
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	13	12
Financing Receivable, before Allowance for Credit Loss	342	501
Single-family [Member] | Adjustable Rate Residential Mortgage [Member] | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	6	56
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	29	3
Financing Receivable, Originated Two Years before Latest Fiscal Year	2	1
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1	2
Financing Receivable, before Allowance for Credit Loss	38	62
Single-family [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	50,800	54,582
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	45
Financing Receivable, Originated Two Years before Latest Fiscal Year	42	360
Financing Receivable, Originated Three Years before Latest Fiscal Year	341	878
Financing Receivable, Originated Four Years before Latest Fiscal Year	826	1,077
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	36,702	38,747
Financing Receivable, before Allowance for Credit Loss	37,911	41,107
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	4
Financing Receivable, Originated Three Years before Latest Fiscal Year	3	8
Financing Receivable, Originated Four Years before Latest Fiscal Year	5	9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	485	631
Financing Receivable, before Allowance for Credit Loss	493	652
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	41
Financing Receivable, Originated Two Years before Latest Fiscal Year	39	328
Financing Receivable, Originated Three Years before Latest Fiscal Year	318	811
Financing Receivable, Originated Four Years before Latest Fiscal Year	779	1,028
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	34,761	36,216
Financing Receivable, before Allowance for Credit Loss	35,897	38,424
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	2
Financing Receivable, Originated Two Years before Latest Fiscal Year	1	20
Financing Receivable, Originated Three Years before Latest Fiscal Year	15	43
Financing Receivable, Originated Four Years before Latest Fiscal Year	31	30
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,000	1,298
Financing Receivable, before Allowance for Credit Loss	1,047	1,393
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	2
Financing Receivable, Originated Two Years before Latest Fiscal Year	2	8
Financing Receivable, Originated Three Years before Latest Fiscal Year	5	16
Financing Receivable, Originated Four Years before Latest Fiscal Year	11	10
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	456	602
Financing Receivable, before Allowance for Credit Loss	474	638
Single-family [Member] | FixedRateResidentialMortgage15yearMember
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	482,469	457,059
Financing Receivable, Originated in Current Fiscal Year	49,496	188,797
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	192,930	42,194
Financing Receivable, Originated Two Years before Latest Fiscal Year	36,271	15,809
Financing Receivable, Originated Three Years before Latest Fiscal Year	13,802	31,518
Financing Receivable, Originated Four Years before Latest Fiscal Year	28,127	46,102
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	161,843	132,639
Financing Receivable, before Allowance for Credit Loss	482,469	457,059
Single-family [Member] | FixedRateResidentialMortgage15yearMember | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	3
Financing Receivable, Originated Three Years before Latest Fiscal Year	2	3
Financing Receivable, Originated Four Years before Latest Fiscal Year	3	3
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	13	13
Financing Receivable, before Allowance for Credit Loss	18	22
Single-family [Member] | FixedRateResidentialMortgage15yearMember | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	48,003	181,418
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	187,390	41,374
Financing Receivable, Originated Two Years before Latest Fiscal Year	35,975	15,768
Financing Receivable, Originated Three Years before Latest Fiscal Year	13,779	31,497
Financing Receivable, Originated Four Years before Latest Fiscal Year	28,112	46,088
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	161,802	132,596
Financing Receivable, before Allowance for Credit Loss	475,061	448,741
Single-family [Member] | FixedRateResidentialMortgage15yearMember | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1,137	6,105
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	4,953	811
Financing Receivable, Originated Two Years before Latest Fiscal Year	292	35
Financing Receivable, Originated Three Years before Latest Fiscal Year	19	14
Financing Receivable, Originated Four Years before Latest Fiscal Year	9	8
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	19	20
Financing Receivable, before Allowance for Credit Loss	6,429	6,993
Single-family [Member] | FixedRateResidentialMortgage15yearMember | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	356	1,274
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	587	9
Financing Receivable, Originated Two Years before Latest Fiscal Year	4	3
Financing Receivable, Originated Three Years before Latest Fiscal Year	2	4
Financing Receivable, Originated Four Years before Latest Fiscal Year	3	3
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	9	10
Financing Receivable, before Allowance for Credit Loss	$ 961	$ 1,303