Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Variable Interest Entities [Line Items]
Trading, at fair value	$ 39,167	$ 39,908
Available-for-sale, at fair value	13,180	20,230
Other assets	19,565	17,553
Other liabilities	(9,372)	(10,393)
Unpaid principal balance of mortgage loans	3,013,878	3,010,753
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	210,678	198,342
Consolidated VIEs [Member]
Variable Interest Entities [Line Items]
Change in assets due to change in consolidation status	166
Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Change in assets due to change in consolidation status		5,100
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	210,700
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	9,356	10,300
Available-for-sale, at fair value	11,838	18,580
Other assets	53	100
Other liabilities	(430)	(827)
Net carrying amount	20,817	28,153
Maximum exposure to loss	26,000	34,000
Total unconsolidated assets	180,000	220,000
Unconsolidated VIEs [Member] | Partnership interest [Member]
Variable Interest Entities [Line Items]
Net carrying amount	93	(24)
Maximum exposure to loss	125	12
Total unconsolidated assets	4,200	4,900
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	5,203	4,704
Available-for-sale, at fair value	3,160	3,936
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,153	5,596
Available-for-sale, at fair value	$ 8,678	$ 14,644