Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	$ 3,368,810	$ 3,336,929
Financing Receivable, before Allowance for Credit Loss	3,367,916	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	9,858
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	69,854
Financing Receivable, Originated Two Years before Latest Fiscal Year	64,740
Financing Receivable, Originated Three Years before Latest Fiscal Year	55,370
Financing Receivable, Originated Four Years before Latest Fiscal Year	47,488
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	90,384
Financing Receivable, before Allowance for Credit Loss	337,694
Fixed Rate Residential Mortgage 30 and 20 year Member | Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		2,517,547
Fixed Rate Residential Mortgage 30 and 20 year 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		2,145,018
Fixed Rate Residential Mortgage 30 and 20 year 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		237,623
Fixed Rate Residential Mortgage 30 and 20 year 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		130,152
Fixed Rate Residential Mortgage 30 and 20 year 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		4,754
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 | Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss		44,908
Adjustable 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		43,415
Adjustable 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		1,275
Adjustable 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		215
Adjustable 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		3
Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	3,031,116	3,006,311
Financing Receivable, Originated in Current Fiscal Year	127,092
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	558,808
Financing Receivable, Originated Two Years before Latest Fiscal Year	295,791
Financing Receivable, Originated Three Years before Latest Fiscal Year	346,087
Financing Receivable, Originated Four Years before Latest Fiscal Year	387,217
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,299,852
Financing Receivable, before Allowance for Credit Loss	3,014,847
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	92,095
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	366,985
Financing Receivable, Originated Two Years before Latest Fiscal Year	205,209
Financing Receivable, Originated Three Years before Latest Fiscal Year	303,352
Financing Receivable, Originated Four Years before Latest Fiscal Year	376,234
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,272,296
Financing Receivable, before Allowance for Credit Loss	2,616,171
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	16,992
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	97,376
Financing Receivable, Originated Two Years before Latest Fiscal Year	73,989
Financing Receivable, Originated Three Years before Latest Fiscal Year	40,407
Financing Receivable, Originated Four Years before Latest Fiscal Year	10,249
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	16,790
Financing Receivable, before Allowance for Credit Loss	255,803
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	18,005
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	94,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	16,432
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,134
Financing Receivable, Originated Four Years before Latest Fiscal Year	538
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	5,939
Financing Receivable, before Allowance for Credit Loss	137,048
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
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	447
Financing Receivable, Originated Two Years before Latest Fiscal Year	161
Financing Receivable, Originated Three Years before Latest Fiscal Year	194
Financing Receivable, Originated Four Years before Latest Fiscal Year	196
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	4,827
Financing Receivable, before Allowance for Credit Loss	5,825
Single-family [Member] | Fixed Rate Residential Mortgage 30 and 20 year Member
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	2,546,890	2,517,547
Financing Receivable, Originated in Current Fiscal Year	110,254
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	494,441
Financing Receivable, Originated Two Years before Latest Fiscal Year	266,896
Financing Receivable, Originated Three Years before Latest Fiscal Year	294,875
Financing Receivable, Originated Four Years before Latest Fiscal Year	323,151
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,057,273
Financing Receivable, before Allowance for Credit Loss	2,546,890
Single-family [Member] | Fixed Rate Residential Mortgage 30 and 20 year 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	76,429
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	307,581
Financing Receivable, Originated Two Years before Latest Fiscal Year	177,622
Financing Receivable, Originated Three Years before Latest Fiscal Year	252,599
Financing Receivable, Originated Four Years before Latest Fiscal Year	312,333
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,034,737
Financing Receivable, before Allowance for Credit Loss	2,161,301
Single-family [Member] | Fixed Rate Residential Mortgage 30 and 20 year 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	16,159
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	93,510
Financing Receivable, Originated Two Years before Latest Fiscal Year	72,787
Financing Receivable, Originated Three Years before Latest Fiscal Year	40,029
Financing Receivable, Originated Four Years before Latest Fiscal Year	10,145
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	14,220
Financing Receivable, before Allowance for Credit Loss	246,850
Single-family [Member] | Fixed Rate Residential Mortgage 30 and 20 year 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	17,666
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	92,907
Financing Receivable, Originated Two Years before Latest Fiscal Year	16,344
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,080
Financing Receivable, Originated Four Years before Latest Fiscal Year	503
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	4,715
Financing Receivable, before Allowance for Credit Loss	134,215
Single-family [Member] | Fixed Rate Residential Mortgage 30 and 20 year 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	443
Financing Receivable, Originated Two Years before Latest Fiscal Year	143
Financing Receivable, Originated Three Years before Latest Fiscal Year	167
Financing Receivable, Originated Four Years before Latest Fiscal Year	170
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	3,601
Financing Receivable, before Allowance for Credit Loss	4,524
Single-family [Member] | FixedRateResidentialMortgage15yearMember
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	375,545	374,087
Financing Receivable, Originated in Current Fiscal Year	16,350
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	61,282
Financing Receivable, Originated Two Years before Latest Fiscal Year	24,019
Financing Receivable, Originated Three Years before Latest Fiscal Year	42,367
Financing Receivable, Originated Four Years before Latest Fiscal Year	58,689
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	172,838
Financing Receivable, before Allowance for Credit Loss	375,545
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	15,233
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	56,811
Financing Receivable, Originated Two Years before Latest Fiscal Year	23,322
Financing Receivable, Originated Three Years before Latest Fiscal Year	42,251
Financing Receivable, Originated Four Years before Latest Fiscal Year	58,651
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	172,743
Financing Receivable, before Allowance for Credit Loss	369,011
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	795
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	3,502
Financing Receivable, Originated Two Years before Latest Fiscal Year	668
Financing Receivable, Originated Three Years before Latest Fiscal Year	97
Financing Receivable, Originated Four Years before Latest Fiscal Year	23
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	46
Financing Receivable, before Allowance for Credit Loss	5,131
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	322
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	967
Financing Receivable, Originated Two Years before Latest Fiscal Year	22
Financing Receivable, Originated Three Years before Latest Fiscal Year	10
Financing Receivable, Originated Four Years before Latest Fiscal Year	8
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	23
Financing Receivable, before Allowance for Credit Loss	1,352
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	2
Financing Receivable, Originated Two Years before Latest Fiscal Year	7
Financing Receivable, Originated Three Years before Latest Fiscal Year	9
Financing Receivable, Originated Four Years before Latest Fiscal Year	7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	26
Financing Receivable, before Allowance for Credit Loss	51
Single-family [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	66,193	69,769
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	49
Financing Receivable, Originated Two Years before Latest Fiscal Year	409
Financing Receivable, Originated Three Years before Latest Fiscal Year	999
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,239
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	47,228
Financing Receivable, before Allowance for Credit Loss	49,924
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	42
Financing Receivable, Originated Two Years before Latest Fiscal Year	348
Financing Receivable, Originated Three Years before Latest Fiscal Year	871
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,134
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	42,367
Financing Receivable, before Allowance for Credit Loss	44,762
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	4
Financing Receivable, Originated Two Years before Latest Fiscal Year	33
Financing Receivable, Originated Three Years before Latest Fiscal Year	73
Financing Receivable, Originated Four Years before Latest Fiscal Year	60
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	2,470
Financing Receivable, before Allowance for Credit Loss	2,640
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	17
Financing Receivable, Originated Three Years before Latest Fiscal Year	37
Financing Receivable, Originated Four Years before Latest Fiscal Year	26
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,193
Financing Receivable, before Allowance for Credit Loss	1,274
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	2
Financing Receivable, Originated Two Years before Latest Fiscal Year	11
Financing Receivable, Originated Three Years before Latest Fiscal Year	18
Financing Receivable, Originated Four Years before Latest Fiscal Year	19
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,198
Financing Receivable, before Allowance for Credit Loss	1,248
Single-family [Member] | Government [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	16,300	17,100
Single-family [Member] | Adjustable Rate Residential Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	42,488	$ 44,908
Financing Receivable, Originated in Current Fiscal Year	488
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	3,036
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,467
Financing Receivable, Originated Three Years before Latest Fiscal Year	7,846
Financing Receivable, Originated Four Years before Latest Fiscal Year	4,138
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	22,513
Financing Receivable, before Allowance for Credit Loss	42,488
Single-family [Member] | Adjustable 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	433
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,551
Financing Receivable, Originated Two Years before Latest Fiscal Year	3,917
Financing Receivable, Originated Three Years before Latest Fiscal Year	7,631
Financing Receivable, Originated Four Years before Latest Fiscal Year	4,116
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	22,449
Financing Receivable, before Allowance for Credit Loss	41,097
Single-family [Member] | Adjustable 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	38
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	360
Financing Receivable, Originated Two Years before Latest Fiscal Year	501
Financing Receivable, Originated Three Years before Latest Fiscal Year	208
Financing Receivable, Originated Four Years before Latest Fiscal Year	21
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	54
Financing Receivable, before Allowance for Credit Loss	1,182
Single-family [Member] | Adjustable 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	17
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	125
Financing Receivable, Originated Two Years before Latest Fiscal Year	49
Financing Receivable, Originated Three Years before Latest Fiscal Year	7
Financing Receivable, Originated Four Years before Latest Fiscal Year	1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	8
Financing Receivable, before Allowance for Credit Loss	207
Single-family [Member] | Adjustable 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
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	2
Financing Receivable, before Allowance for Credit Loss	$ 2