Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entities [Line Items]
Trading, at fair value	$ 41,867	$ 34,679
Available-for-sale securities	3,429	4,843
Other assets	17,004	19,049
Other liabilities	(9,947)	(9,479)
Unpaid principal balance of mortgage loans	3,223,783	3,155,703
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	293,858	265,069
Consolidated VIEs [Member]
Variable Interest Entities [Line Items]
Other liabilities	(356)	(492)
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Total unconsolidated assets	931
Unpaid principal balance of mortgage loans	293,900
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	1,422	3,809
Available-for-sale securities	1,704	2,032
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,809	1,580
Available-for-sale securities	1,207	2,062
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	6,231	5,389
Available-for-sale securities	2,911	4,094
Other assets	66	74
Other liabilities	(101)	(467)
Net carrying amount	9,107	9,090
Maximum exposure to loss	14,000	15,000
Total unconsolidated assets	80,000	70,000
Unconsolidated VIEs [Member] | Partnership Interest [Member]
Variable Interest Entities [Line Items]
Net carrying amount	89	82
Maximum exposure to loss	111	105
Total unconsolidated assets	2,300	$ 3,200
Unconsolidated VIEs [Member] | Debt Securities [Member]
Variable Interest Entities [Line Items]
Maximum exposure to loss	$ 920