Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entities [Line Items]
Trading, at fair value	$ 40,562	$ 39,908
Available-for-sale securities	8,363	20,230
Other assets	20,942	17,553
Other liabilities	(10,150)	(10,393)
Unpaid principal balance of mortgage loans	3,063,646	3,010,753
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	229,896	198,342
Consolidated VIEs [Member]
Variable Interest Entities [Line Items]
Change in assets due to change in consolidation status	145
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	229,900
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,642	4,704
Available-for-sale securities	2,447	3,936
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	3,473	5,596
Available-for-sale securities	4,879	14,644
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	8,115	10,300
Available-for-sale securities	7,326	18,580
Other assets	77	100
Other liabilities	(528)	(827)
Net carrying amount	14,990	28,153
Maximum exposure to loss	21,000	34,000
Total unconsolidated assets	150,000	220,000
Unconsolidated VIEs [Member] | Partnership Interest [Member]
Variable Interest Entities [Line Items]
Net carrying amount	92	(24)
Maximum exposure to loss	118	12
Total unconsolidated assets	$ 3,900	$ 4,900