Consolidations and Transfers of Financial Assets - Unconsolidated VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Variable Interest Entities [Line Items]
Trading, at fair value	$ 95,101	$ 136,542
Available-for-sale, at fair value	955	1,697
Other assets	11,349	15,201
Other liabilities	(15,044)	(15,035)
Assets	4,158,038	3,985,749
Total unpaid principal balance of mortgage loans	3,782,552	3,589,868
Multifamily
Variable Interest Entities [Line Items]
Total unpaid principal balance of mortgage loans	391,725	373,722
Multifamily | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Total unpaid principal balance of mortgage loans	391,700
Single-family
Variable Interest Entities [Line Items]
Total unpaid principal balance of mortgage loans	3,390,827	3,216,146
Mortgage-related securities | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Trading, at fair value	4,631	5,219
Available-for-sale, at fair value	786	1,486
Other assets	38	41
Other liabilities	(63)	(67)
Net carrying amount	5,392	6,679
Maximum exposure to loss	177,000	146,000
Assets	230,000	180,000
Partnership interest LIHTC [Member] | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Net carrying amount	190	121
Maximum exposure to loss	195	126
Assets	3,200	2,600
Debt Securities [Member] | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Maximum exposure to loss	9,100	11,400
Assets	9,100	11,400
Fannie Mae Securities [Member] | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Trading, at fair value	1,146	1,611
Available-for-sale, at fair value	562	1,168
Non-Fannie Mae Securities [Member] | Unconsolidated VIEs
Variable Interest Entities [Line Items]
Trading, at fair value	3,485	3,608
Available-for-sale, at fair value	$ 224	$ 318