Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	$ 3,467,079	$ 3,336,929
Financing Receivable, before Allowance for Credit Loss	3,464,721	3,336,405
Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		2,989,182
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, before Allowance for Credit Loss		2,603,619
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, before Allowance for Credit Loss		246,326
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, before Allowance for Credit Loss		133,049
Single-family [Member] | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		6,188
Multifamily [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	29,928
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	69,756
Financing Receivable, Originated Two Years before Latest Fiscal Year	64,409
Financing Receivable, Originated Three Years before Latest Fiscal Year	54,986
Financing Receivable, Originated Four Years before Latest Fiscal Year	46,877
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	84,688
Financing Receivable, before Allowance for Credit Loss	350,644
FixedRateResidentialMortgage15yearMember | Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		374,087
FixedRateResidentialMortgage15yearMember | 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, before Allowance for Credit Loss		368,181
FixedRateResidentialMortgage15yearMember | 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, before Allowance for Credit Loss		4,556
FixedRateResidentialMortgage15yearMember | 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, before Allowance for Credit Loss		1,284
FixedRateResidentialMortgage15yearMember | Single-family [Member] | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		66
Other [Member] | Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		52,640
Other [Member] | 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, before Allowance for Credit Loss		47,005
Other [Member] | 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, before Allowance for Credit Loss		2,872
Other [Member] | 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, before Allowance for Credit Loss		1,398
Other [Member] | Single-family [Member] | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		1,365
Adjustable Rate Residential Mortgage [Member] | Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		44,908
Adjustable Rate Residential Mortgage [Member] | 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, before Allowance for Credit Loss		43,415
Adjustable Rate Residential Mortgage [Member] | 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, before Allowance for Credit Loss		1,275
Adjustable Rate Residential Mortgage [Member] | 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, before Allowance for Credit Loss		215
Adjustable Rate Residential Mortgage [Member] | Single-family [Member] | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		3
Fixed Rate Residential Mortgage | Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		2,517,547
Fixed Rate Residential Mortgage | 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, before Allowance for Credit Loss		2,145,018
Fixed Rate Residential Mortgage | 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, before Allowance for Credit Loss		237,623
Fixed Rate Residential Mortgage | 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, before Allowance for Credit Loss		130,152
Fixed Rate Residential Mortgage | Single-family [Member] | Estimated mark-to-market loan-to-value ratio greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		4,754
Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	3,116,435	3,006,311
Financing Receivable, Originated in Current Fiscal Year	484,429
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	503,625
Financing Receivable, Originated Two Years before Latest Fiscal Year	249,724
Financing Receivable, Originated Three Years before Latest Fiscal Year	305,342
Financing Receivable, Originated Four Years before Latest Fiscal Year	354,198
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,203,489
Financing Receivable, before Allowance for Credit Loss	3,100,807
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	362,234
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	347,950
Financing Receivable, Originated Two Years before Latest Fiscal Year	186,278
Financing Receivable, Originated Three Years before Latest Fiscal Year	282,303
Financing Receivable, Originated Four Years before Latest Fiscal Year	348,477
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,182,131
Financing Receivable, before Allowance for Credit Loss	2,709,373
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	62,376
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	105,570
Financing Receivable, Originated Two Years before Latest Fiscal Year	58,965
Financing Receivable, Originated Three Years before Latest Fiscal Year	22,037
Financing Receivable, Originated Four Years before Latest Fiscal Year	5,284
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	12,590
Financing Receivable, before Allowance for Credit Loss	266,822
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	59,809
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	50,049
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,406
Financing Receivable, Originated Three Years before Latest Fiscal Year	849
Financing Receivable, Originated Four Years before Latest Fiscal Year	282
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	4,781
Financing Receivable, before Allowance for Credit Loss	120,176
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	10
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	56
Financing Receivable, Originated Two Years before Latest Fiscal Year	75
Financing Receivable, Originated Three Years before Latest Fiscal Year	153
Financing Receivable, Originated Four Years before Latest Fiscal Year	155
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	3,987
Financing Receivable, before Allowance for Credit Loss	4,436
Single-family [Member] | FixedRateResidentialMortgage15yearMember
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	401,385	374,087
Financing Receivable, Originated in Current Fiscal Year	70,475
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	55,672
Financing Receivable, Originated Two Years before Latest Fiscal Year	20,944
Financing Receivable, Originated Three Years before Latest Fiscal Year	39,108
Financing Receivable, Originated Four Years before Latest Fiscal Year	55,101
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	160,085
Financing Receivable, before Allowance for Credit Loss	401,385
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	66,148
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	52,825
Financing Receivable, Originated Two Years before Latest Fiscal Year	20,646
Financing Receivable, Originated Three Years before Latest Fiscal Year	39,058
Financing Receivable, Originated Four Years before Latest Fiscal Year	55,074
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	160,012
Financing Receivable, before Allowance for Credit Loss	393,763
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	3,234
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,578
Financing Receivable, Originated Two Years before Latest Fiscal Year	287
Financing Receivable, Originated Three Years before Latest Fiscal Year	35
Financing Receivable, Originated Four Years before Latest Fiscal Year	16
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	35
Financing Receivable, before Allowance for Credit Loss	6,185
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	1,093
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	269
Financing Receivable, Originated Two Years before Latest Fiscal Year	6
Financing Receivable, Originated Three Years before Latest Fiscal Year	8
Financing Receivable, Originated Four Years before Latest Fiscal Year	5
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	16
Financing Receivable, before Allowance for Credit Loss	1,397
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
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	5
Financing Receivable, Originated Three Years before Latest Fiscal Year	7
Financing Receivable, Originated Four Years before Latest Fiscal Year	6
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	22
Financing Receivable, before Allowance for Credit Loss	40
Single-family [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	63,526	69,769
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	48
Financing Receivable, Originated Two Years before Latest Fiscal Year	398
Financing Receivable, Originated Three Years before Latest Fiscal Year	968
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,197
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	45,287
Financing Receivable, before Allowance for Credit Loss	47,898
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
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	43
Financing Receivable, Originated Two Years before Latest Fiscal Year	347
Financing Receivable, Originated Three Years before Latest Fiscal Year	859
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,112
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	41,160
Financing Receivable, before Allowance for Credit Loss	43,521
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
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	3
Financing Receivable, Originated Two Years before Latest Fiscal Year	29
Financing Receivable, Originated Three Years before Latest Fiscal Year	65
Financing Receivable, Originated Four Years before Latest Fiscal Year	48
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	2,101
Financing Receivable, before Allowance for Credit Loss	2,246
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
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1
Financing Receivable, Originated Two Years before Latest Fiscal Year	14
Financing Receivable, Originated Three Years before Latest Fiscal Year	28
Financing Receivable, Originated Four Years before Latest Fiscal Year	22
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,011
Financing Receivable, before Allowance for Credit Loss	1,076
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
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1
Financing Receivable, Originated Two Years before Latest Fiscal Year	8
Financing Receivable, Originated Three Years before Latest Fiscal Year	16
Financing Receivable, Originated Four Years before Latest Fiscal Year	15
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,015
Financing Receivable, before Allowance for Credit Loss	1,055
Single-family [Member] | Government [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss	15,600	17,100
Single-family [Member] | Adjustable Rate Residential Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	39,574	44,908
Financing Receivable, Originated in Current Fiscal Year	2,064
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,732
Financing Receivable, Originated Two Years before Latest Fiscal Year	3,756
Financing Receivable, Originated Three Years before Latest Fiscal Year	6,924
Financing Receivable, Originated Four Years before Latest Fiscal Year	3,720
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	20,378
Financing Receivable, before Allowance for Credit Loss	39,574
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	1,834
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,390
Financing Receivable, Originated Two Years before Latest Fiscal Year	3,428
Financing Receivable, Originated Three Years before Latest Fiscal Year	6,818
Financing Receivable, Originated Four Years before Latest Fiscal Year	3,706
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	20,340
Financing Receivable, before Allowance for Credit Loss	38,516
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	163
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	287
Financing Receivable, Originated Two Years before Latest Fiscal Year	319
Financing Receivable, Originated Three Years before Latest Fiscal Year	101
Financing Receivable, Originated Four Years before Latest Fiscal Year	14
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	32
Financing Receivable, before Allowance for Credit Loss	916
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	67
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	55
Financing Receivable, Originated Two Years before Latest Fiscal Year	9
Financing Receivable, Originated Three Years before Latest Fiscal Year	5
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	5
Financing Receivable, before Allowance for Credit Loss	141
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
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1
Financing Receivable, before Allowance for Credit Loss	1
Single-family [Member] | Fixed Rate Residential Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	2,611,950	$ 2,517,547
Financing Receivable, Originated in Current Fiscal Year	411,890
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	445,173
Financing Receivable, Originated Two Years before Latest Fiscal Year	224,626
Financing Receivable, Originated Three Years before Latest Fiscal Year	258,342
Financing Receivable, Originated Four Years before Latest Fiscal Year	294,180
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	977,739
Financing Receivable, before Allowance for Credit Loss	2,611,950
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	294,252
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	292,692
Financing Receivable, Originated Two Years before Latest Fiscal Year	161,857
Financing Receivable, Originated Three Years before Latest Fiscal Year	235,568
Financing Receivable, Originated Four Years before Latest Fiscal Year	288,585
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	960,619
Financing Receivable, before Allowance for Credit Loss	2,233,573
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	58,979
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	102,702
Financing Receivable, Originated Two Years before Latest Fiscal Year	58,330
Financing Receivable, Originated Three Years before Latest Fiscal Year	21,836
Financing Receivable, Originated Four Years before Latest Fiscal Year	5,206
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	10,422
Financing Receivable, before Allowance for Credit Loss	257,475
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	58,649
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	49,724
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,377
Financing Receivable, Originated Three Years before Latest Fiscal Year	808
Financing Receivable, Originated Four Years before Latest Fiscal Year	255
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	3,749
Financing Receivable, before Allowance for Credit Loss	117,562
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	10
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	55
Financing Receivable, Originated Two Years before Latest Fiscal Year	62
Financing Receivable, Originated Three Years before Latest Fiscal Year	130
Financing Receivable, Originated Four Years before Latest Fiscal Year	134
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	2,949
Financing Receivable, before Allowance for Credit Loss	$ 3,340