Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Variable Interest Entities [Line Items]
Trading, at fair value	$ 40,547	$ 39,908
Available-for-sale, at fair value	9,865	20,230
Other assets	20,864	17,553
Other liabilities	(9,141)	(10,393)
Unpaid principal balance of mortgage loans	3,029,642	3,010,753
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	221,860	198,342
Consolidated VIEs [Member]
Variable Interest Entities [Line Items]
Change in assets due to change in consolidation status	154
Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Change in assets due to change in consolidation status		5,300
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	221,900
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	9,129	10,300
Available-for-sale, at fair value	8,707	18,580
Other assets	67	100
Other liabilities	(450)	(827)
Net carrying amount	17,453	28,153
Maximum exposure to loss	24,000	34,000
Total unconsolidated assets	170,000	220,000
Unconsolidated VIEs [Member] | Partnership interest [Member]
Variable Interest Entities [Line Items]
Net carrying amount	92	(24)
Maximum exposure to loss	123	12
Total unconsolidated assets	4,000	4,900
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,793	4,704
Available-for-sale, at fair value	2,601	3,936
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,336	5,596
Available-for-sale, at fair value	$ 6,106	$ 14,644