Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entities [Line Items]
Trading, at fair value	$ 48,123	$ 41,867
Available-for-sale securities	2,404	3,429
Other assets	20,765	17,004
Other liabilities	(11,097)	(9,947)
Unpaid principal balance of mortgage loans	3,299,954	3,223,783
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	327,593	293,858
Consolidated VIEs [Member]
Variable Interest Entities [Line Items]
Other liabilities	(376)	(356)
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	327,600
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	2,543	1,422
Available-for-sale securities	1,524	1,704
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	5,100	4,809
Available-for-sale securities	574	1,207
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	7,643	6,231
Available-for-sale securities	2,098	2,911
Other assets	56	66
Other liabilities	(78)	(101)
Net carrying amount	9,719	9,107
Maximum exposure to loss	62,000	14,000
Total unconsolidated assets	130,000	80,000
Unconsolidated VIEs [Member] | Partnership Interest [Member]
Variable Interest Entities [Line Items]
Net carrying amount	79	89
Maximum exposure to loss	98	111
Total unconsolidated assets	2,000	2,300
Unconsolidated VIEs [Member] | Debt Securities [Member]
Variable Interest Entities [Line Items]
Maximum exposure to loss	9,500	920
Total unconsolidated assets	$ 9,500	$ 931