Fair Value - Level 3 Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Total available-for-sale securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 693	$ 452	$ 753	$ 648
Total gains (losses) (realized/unrealized) included in net income	(1)	3	(8)	11
Total gains (losses) (realized/unrealized) Included in OCI (loss)	0	(6)	(6)	(4)
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(18)	(29)	(64)	(128)
Transfers out of Level 3	0	0	(2)	(107)
Transfers into Level 3	0	376	1	376
Ending Balance	674	796	674	796
Net unrealized gain (losses) related to assets	1	(4)	(4)	(1)
Mortgage loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	599	832	755	861
Total gains (losses) (realized/unrealized) included in net income	(20)	1	(68)	30
Total gains (losses) (realized/unrealized) Included in OCI (loss)	0	0	0	0
Purchases	0	4	0	89
Sales	0	(4)	(2)	(48)
Issues	0	0	0	0
Settlements	(33)	(47)	(115)	(147)
Transfers out of Level 3	(13)	(20)	(73)	(72)
Transfers into Level 3	12	19	48	72
Ending Balance	545	785	545	785
Net unrealized gain (losses) related to assets	(21)	3	(59)	28
Net derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(7)	194	131	333
Total gains (losses) (realized/unrealized) included in net income	(26)	(62)	(183)	(187)
Total gains (losses) (realized/unrealized) Included in OCI (loss)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	1	7	20	(7)
Transfers out of Level 3	0	0	0	0
Transfers into Level 3	0	0	0	0
Ending Balance	(32)	139	(32)	139
Net unrealized gain (losses) related to assets	(25)	(55)	(163)	(194)
Long-term debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(405)	(452)	(468)	(499)
Total gains (losses) (realized/unrealized) included in net income	3	6	125	26
Total gains (losses) (realized/unrealized) included in OCI (loss)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	(86)	0
Settlements	7	2	34	10
Transfers out of Level 3	0	0	1	20
Transfers into Level 3	0	(45)	(1)	(46)
Ending Balance	(395)	(489)	(395)	(489)
Net unrealized gain (losses) related to liabilities	2	7	125	25
Fannie Mae | Long-term debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(253)	(397)	(373)	(416)
Total gains (losses) (realized/unrealized) included in net income	(1)	9	119	28
Total gains (losses) (realized/unrealized) included in OCI (loss)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	0	0	0	0
Transfers out of Level 3	0	0	0	0
Transfers into Level 3	0	0	0	0
Ending Balance	(254)	(388)	(254)	(388)
Net unrealized gain (losses) related to liabilities	(1)	9	119	28
Consolidated Trusts | Long-term debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(152)	(55)	(95)	(83)
Total gains (losses) (realized/unrealized) included in net income	4	(3)	6	(2)
Total gains (losses) (realized/unrealized) included in OCI (loss)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	(86)	0
Settlements	7	2	34	10
Transfers out of Level 3	0	0	1	20
Transfers into Level 3	0	(45)	(1)	(46)
Ending Balance	(141)	(101)	(141)	(101)
Net unrealized gain (losses) related to liabilities	3	(2)	6	(3)
Mortgage-related securities | Total trading securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	76	141	57	95
Total gains (losses) (realized/unrealized) included in net income	(3)	(13)	(11)	(18)
Total gains (losses) (realized/unrealized) Included in OCI (loss)	0	0	0	0
Purchases	0	15	0	18
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	0	0	(1)	0
Transfers out of Level 3	(33)	(51)	(47)	(91)
Transfers into Level 3	0	37	42	125
Ending Balance	40	129	40	129
Net unrealized gain (losses) related to assets	2	0	(2)	1
Agency securities | Total available-for-sale securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	404	84	431	195
Total gains (losses) (realized/unrealized) included in net income	1	0	2	1
Total gains (losses) (realized/unrealized) Included in OCI (loss)	(1)	2	(5)	4
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(11)	(12)	(35)	(19)
Transfers out of Level 3	0	0	0	(107)
Transfers into Level 3	0	376	0	376
Ending Balance	393	450	393	450
Net unrealized gain (losses) related to assets	(1)	0	(4)	1
Other mortgage-related | Total available-for-sale securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	289	368	322	453
Total gains (losses) (realized/unrealized) included in net income	(2)	3	(10)	10
Total gains (losses) (realized/unrealized) Included in OCI (loss)	1	(8)	(1)	(8)
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(7)	(17)	(29)	(109)
Transfers out of Level 3	0	0	(2)	0
Transfers into Level 3	0	0	1	0
Ending Balance	281	346	281	346
Net unrealized gain (losses) related to assets	$ 2	$ (4)	$ 0	$ (2)