Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Variable Interest Entities [Line Items]
Trading, at fair value	$ 44,206	$ 41,867
Available-for-sale, at fair value	2,690	3,429
Other assets	22,361	17,004
Other liabilities	$ (11,836)	(9,947)
Document Period End Date	Sep. 30, 2019
Unpaid principal balance of mortgage loans	$ 3,280,189	3,223,783
Unpaid Principal Balance of Loans Securitized in Unconsolidated Portfolio Securitization Trusts	1,100	1,200
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	318,106	293,858
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	6,500	931
Unpaid principal balance of mortgage loans	318,100
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	7,178	6,231
Available-for-sale, at fair value	2,352	2,911
Other assets	57	66
Other liabilities	(82)	(101)
Net carrying amount	9,505	9,107
Maximum exposure to loss	41,000	14,000
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	100,000	80,000
Unconsolidated VIEs [Member] | Partnership interest LIHTC [Member]
Variable Interest Entities [Line Items]
Net carrying amount	70	89
Maximum exposure to loss	93
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	2,300	2,300
Unconsolidated VIEs [Member] | Debt Securities [Member]
Variable Interest Entities [Line Items]
Maximum exposure to loss	6,500	920
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	2,733	1,422
Available-for-sale, at fair value	1,581	1,704
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	4,445	4,809
Available-for-sale, at fair value	$ 771	$ 1,207