Consolidations and Transfers of Financial Assets - Unconsolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entities [Line Items]
Trading, at fair value	$ 97,209	$ 136,542
Available-for-sale, at fair value	886	1,697
Other assets	12,163	15,201
Other liabilities	(15,268)	(15,035)
Assets	4,209,209	3,985,749
Total unpaid principal balance of mortgage loans	3,833,191	3,589,868
Multifamily
Variable Interest Entities [Line Items]
Total unpaid principal balance of mortgage loans	398,168	373,722
Multifamily | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Total unpaid principal balance of mortgage loans	398,200
Single-family
Variable Interest Entities [Line Items]
Total unpaid principal balance of mortgage loans	3,435,023	3,216,146
Mortgage-related securities | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Trading, at fair value	4,355	5,219
Available-for-sale, at fair value	725	1,486
Other assets	37	41
Other liabilities	(63)	(67)
Net carrying amount	5,054	6,679
Maximum exposure to loss	198,000	146,000
Assets	240,000	180,000
Partnership interest LIHTC | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Net carrying amount	219	121
Maximum exposure to loss	225	126
Assets	3,300	2,600
Debt securities | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Maximum exposure to loss	8,200	11,400
Assets	8,200	11,400
Fannie Mae securities | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Trading, at fair value	1,073	1,611
Available-for-sale, at fair value	518	1,168
Non-Fannie Mae securities | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Trading, at fair value	3,282	3,608
Available-for-sale, at fair value	$ 207	$ 318