Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Trading, at fair value	$ 136,542		$ 48,123
Available-for-sale securities	1,697		2,404
Other assets	15,201	$ 14,542	14,312
Other liabilities	(15,035)		(11,097)
Unpaid principal balance of mortgage loans	3,589,868		3,299,954
Assets	3,985,749		3,503,319
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	373,722		327,593
Multifamily [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	373,700
Fannie Mae Securities [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	1,611		2,543
Available-for-sale securities	1,168		1,524
Non-Fannie Mae Securities [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	3,608		5,100
Available-for-sale securities	318		574
Mortgage-related securities [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	5,219		7,643
Available-for-sale securities	1,486		2,098
Other assets	41		56
Other liabilities	(67)		(78)
Net Assets	6,679		9,719
Maximum exposure to loss	146,000		62,000
Assets	180,000		130,000
Partnership Interest [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Net Assets	121		79
Maximum exposure to loss	126		98
Assets	2,600		2,000
Debt Securities [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Maximum exposure to loss	11,400		9,500
Assets	$ 11,400		$ 9,500