Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Variable Interest Entities [Line Items]
Trading, at fair value	$ 37,684	$ 40,562
Available-for-sale, at fair value	7,721	8,363
Other assets	16,824	20,942
Other liabilities	(9,133)	(10,150)
Unpaid principal balance of mortgage loans	3,093,430	3,063,646
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	240,691	229,896
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	240,700
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	7,387	8,115
Available-for-sale, at fair value	6,763	7,326
Other assets	73	77
Other liabilities	(555)	(528)
Net carrying amount	13,668	14,990
Maximum exposure to loss	19,000	21,000
Total unconsolidated assets	120,000	150,000
Unconsolidated VIEs [Member] | Partnership interest [Member]
Variable Interest Entities [Line Items]
Net carrying amount	86	92
Maximum exposure to loss	110	118
Total unconsolidated assets	3,900	3,900
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,455	4,642
Available-for-sale, at fair value	2,261	2,447
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	2,932	3,473
Available-for-sale, at fair value	$ 4,502	$ 4,879