Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jan. 01, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Assets	$ 3,760,676		$ 3,760,676			$ 3,503,319
Trading, at fair value	106,744		106,744			48,123
Available-for-sale, at fair value	2,120		2,120			2,404
Other assets	14,178		14,178		$ 14,542	14,312
Other liabilities	(14,170)		(14,170)			(11,097)
Unpaid principal balance of mortgage loans	3,417,834		3,417,834			3,299,954
Portfolio securitizations: unpaid principal balance	202,900	$ 57,300	291,900	$ 98,700
Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Retained interests: principal and interest received	170	$ 122	351	$ 238
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	346,932		346,932			327,593
Multifamily [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	346,900		346,900
Single-family [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	3,070,902		3,070,902			2,972,361
Mortgage-related securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Assets	170,000		170,000			130,000
Trading, at fair value	9,805		9,805			7,643
Available-for-sale, at fair value	1,847		1,847			2,098
Other assets	43		43			56
Other liabilities	(69)		(69)			(78)
Maximum exposure to loss	111,000		111,000			62,000
Net carrying amount	11,626		11,626			9,719
Partnership interest LIHTC [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Assets	1,600		1,600			2,000
Maximum exposure to loss	94		94			98
Net carrying amount	87		87			79
Debt Securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Assets	11,200		11,200			9,500
Maximum exposure to loss	11,200		11,200			9,500
Fannie Mae Securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	6,224		6,224			2,543
Available-for-sale, at fair value	1,395		1,395			1,524
Non-Fannie Mae Securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	3,581		3,581			5,100
Available-for-sale, at fair value	$ 452		$ 452			$ 574