Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jan. 01, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Assets	$ 3,864,603		$ 3,864,603			$ 3,503,319
Trading, at fair value	142,472		142,472			48,123
Available-for-sale, at fair value	1,895		1,895			2,404
Other assets	14,959		14,959		$ 14,542	14,312
Other liabilities	(14,124)		(14,124)			(11,097)
Unpaid principal balance of mortgage loans	3,493,676		3,493,676			3,299,954
Portfolio securitizations: unpaid principal balance	213,000	$ 89,000	504,900	$ 187,700
Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Retained interests: principal and interest received	166	$ 187	517	$ 425
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	355,950		355,950			327,593
Multifamily [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	356,000		356,000
Single-family [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	3,137,726		3,137,726			2,972,361
Mortgage-related securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Assets	190,000		190,000			130,000
Trading, at fair value	5,576		5,576			7,643
Available-for-sale, at fair value	1,645		1,645			2,098
Other assets	42		42			56
Other liabilities	(68)		(68)			(78)
Maximum exposure to loss	127,000		127,000			62,000
Net carrying amount	7,195		7,195			9,719
Partnership interest LIHTC [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Assets	2,300		2,300			2,000
Maximum exposure to loss	107		107			98
Net carrying amount	99		99			79
Debt Securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Assets	10,100		10,100			9,500
Maximum exposure to loss	10,100		10,100			9,500
Fannie Mae Securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	1,900		1,900			2,543
Available-for-sale, at fair value	1,284		1,284			1,524
Non-Fannie Mae Securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	3,676		3,676			5,100
Available-for-sale, at fair value	$ 361		$ 361			$ 574