Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Variable Interest Entities [Line Items]
Assets	$ 4,070,103		$ 3,985,749
Trading, at fair value	111,256		136,542
Available-for-sale, at fair value	1,502		1,697
Other assets	13,923		15,201
Other liabilities	(16,313)		(15,035)
Unpaid principal balance of mortgage loans	3,674,972		3,589,868
Portfolio securitizations: unpaid principal balance	216,700	$ 89,000
Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Retained interests: principal and interest received	143	$ 181
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	388,591		373,722
Multifamily [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	388,600
Single-family [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	3,286,381		3,216,146
Mortgage-related securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Assets	230,000		180,000
Trading, at fair value	4,841		5,219
Available-for-sale, at fair value	1,315		1,486
Other assets	39		41
Other liabilities	(65)		(67)
Maximum exposure to loss	164,000		146,000
Net carrying amount	6,130		6,679
Partnership interest LIHTC [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Assets	2,500		2,600
Maximum exposure to loss	169		126
Net carrying amount	163		121
Debt Securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Assets	10,500		11,400
Maximum exposure to loss	10,400		11,400
Fannie Mae Securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	1,243		1,611
Available-for-sale, at fair value	1,036		1,168
Non-Fannie Mae Securities [Member] | Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	3,598		3,608
Available-for-sale, at fair value	$ 279		$ 318