Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Variable Interest Entities [Line Items]
Trading, at fair value	$ 39,274	$ 40,562
Available-for-sale, at fair value	6,408	8,363
Other assets	18,072	20,942
Other liabilities	(8,373)	(10,150)
Unpaid principal balance of mortgage loans	3,105,954	3,063,646
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	244,701	229,896
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	244,700
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	6,774	8,115
Available-for-sale, at fair value	5,493	7,326
Other assets	74	77
Other liabilities	(501)	(528)
Net carrying amount	11,840	14,990
Maximum exposure to loss	17,000	21,000
Total unconsolidated assets	100,000	150,000
Unconsolidated VIEs [Member] | Partnership interest [Member]
Variable Interest Entities [Line Items]
Net carrying amount	83	92
Maximum exposure to loss	108	118
Total unconsolidated assets	3,600	3,900
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,197	4,642
Available-for-sale, at fair value	2,174	2,447
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	2,577	3,473
Available-for-sale, at fair value	$ 3,319	$ 4,879