Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Trading, at fair value	$ 52,941		$ 48,123
Available-for-sale, at fair value	2,289		2,404
Other assets	13,999	$ 14,542	14,312
Other liabilities	(14,609)		(11,097)
Unpaid principal balance of mortgage loans	3,330,678		3,299,954
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	334,397		327,593
Single-family [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	(2,996,281)		2,972,361
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	334,400
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	7,276		7,643
Available-for-sale, at fair value	1,998		2,098
Other assets	45		56
Other liabilities	(71)		(78)
Maximum exposure to loss	84,000		62,000
Net carrying amount	9,248		9,719
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	170,000		130,000
Unconsolidated VIEs [Member] | Partnership interest LIHTC [Member]
Variable Interest Entities [Line Items]
Maximum exposure to loss	93
Net carrying amount	75		79
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	1,700		2,000
Unconsolidated VIEs [Member] | Debt Securities [Member]
Variable Interest Entities [Line Items]
Maximum exposure to loss	12,300		9,500
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	12,400		9,500
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	2,666		2,543
Available-for-sale, at fair value	1,505		1,524
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,610		5,100
Available-for-sale, at fair value	$ 493		$ 574