Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entities [Line Items]
Trading, at fair value	$ 40,899	$ 41,867
Available-for-sale, at fair value	3,214	3,429
Other assets	17,839	17,004
Other liabilities	(10,299)	(9,947)
Unpaid principal balance of mortgage loans	3,232,801	3,223,783
Principal Amount Outstanding on Loans Securitized or Asset-backed Financing Arrangement	1,200	1,200
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	302,152	293,858
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Total unconsolidated assets	2,900	931
Unpaid principal balance of mortgage loans	302,200
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	5,755	6,231
Available-for-sale, at fair value	2,706	2,911
Other assets	65	66
Other liabilities	(97)	(101)
Net carrying amount	8,429	9,107
Maximum exposure to loss	13,000	14,000
Total unconsolidated assets	70,000	80,000
Unconsolidated VIEs [Member] | Partnership interest [Member]
Variable Interest Entities [Line Items]
Net carrying amount	82	89
Maximum exposure to loss	103	111
Total unconsolidated assets	2,300	2,300
Unconsolidated VIEs [Member] | Debt Securities [Member]
Variable Interest Entities [Line Items]
Maximum exposure to loss	2,900	920
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	1,543	1,422
Available-for-sale, at fair value	1,660	1,704
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,212	4,809
Available-for-sale, at fair value	$ 1,046	$ 1,207