Fair Value - Level 3 Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Total trading securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 47	$ 109	$ 57	$ 95
Total gains (losses) (realized/unrealized) Included in Net Income	(2)	(4)	(8)	(5)
Total gains (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0	0
Purchases	0	3	0	3
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(1)	0	(1)	0
Transfers out of Level 3	(5)	(32)	(14)	(40)
Transfers into Level 3	37	65	42	88
Ending Balance	76	141	76	141
Net unrealized gain (losses) related to assets	(1)	1	(3)	2
Total trading securities | Fannie Mae
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	47	109	57	94
Total gains (losses) (realized/unrealized) Included in Net Income	(2)	(4)	(8)	(5)
Total gains (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0	0
Purchases	0	3	0	3
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(1)	0	(1)	0
Transfers out of Level 3	(5)	(32)	(14)	(39)
Transfers into Level 3	37	65	42	88
Ending Balance	76	141	76	141
Net unrealized gain (losses) related to assets	(1)	1	(3)	2
Total trading securities | Other agency
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				1
Total gains (losses) (realized/unrealized) Included in Net Income				0
Total gains (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)				0
Purchases				0
Sales				0
Issues				0
Settlements				0
Transfers out of Level 3				(1)
Transfers into Level 3				0
Ending Balance		0		0
Net unrealized gain (losses) related to assets				0
Total available-for-sale securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	727	611	753	648
Total gains (losses) (realized/unrealized) Included in Net Income	0	5	(7)	8
Total gains (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	(1)	4	(6)	2
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(33)	(61)	(46)	(99)
Transfers out of Level 3	0	(107)	(2)	(107)
Transfers into Level 3	0	0	1	0
Ending Balance	693	452	693	452
Net unrealized gain (losses) related to assets	0	0	0	0
Total available-for-sale securities | Fannie Mae
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	418	189	431	195
Total gains (losses) (realized/unrealized) Included in Net Income	0	1	1	1
Total gains (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	5	(4)	2
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(14)	(4)	(24)	(7)
Transfers out of Level 3	0	(107)	0	(107)
Transfers into Level 3	0	0	0	0
Ending Balance	404	84	404	84
Net unrealized gain (losses) related to assets	0	0	0	0
Total available-for-sale securities | Other securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	309	422	322	453
Total gains (losses) (realized/unrealized) Included in Net Income	0	4	(8)	7
Total gains (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	(1)	(1)	(2)	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(19)	(57)	(22)	(92)
Transfers out of Level 3	0	0	(2)	0
Transfers into Level 3	0	0	1	0
Ending Balance	289	368	289	368
Net unrealized gain (losses) related to assets	0	0	0	0
Mortgage loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	668	820	755	861
Total gains (losses) (realized/unrealized) Included in Net Income	(23)	21	(48)	29
Total gains (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0	0
Purchases	0	85	0	85
Sales	(2)	(44)	(2)	(44)
Issues	0	0	0	0
Settlements	(41)	(53)	(82)	(100)
Transfers out of Level 3	(16)	(29)	(60)	(52)
Transfers into Level 3	13	32	36	53
Ending Balance	599	832	599	832
Net unrealized gain (losses) related to assets	(23)	22	(42)	28
Net derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	57	166	131	333
Total gains (losses) (realized/unrealized) Included in Net Income	(75)	7	(157)	(125)
Total gains (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	11	21	19	(14)
Transfers out of Level 3	0	0	0	0
Transfers into Level 3	0	0	0	0
Ending Balance	(7)	194	(7)	194
Net unrealized gain (losses) related to assets	(64)	28	(138)	(139)
Long-term debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(468)	(440)	(468)	(499)
Total gains (losses) (realized/unrealized) Included in Net Income	54	(15)	122	20
Total gains (losses) (realized/unrealized) included in OCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	(86)	0
Settlements	9	4	27	8
Transfers out of Level 3	0	0	1	20
Transfers into Level 3	0	(1)	(1)	(1)
Ending Balance	(405)	(452)	(405)	(452)
Net unrealized gain (losses) related to liabilities	55	(15)	123	19
Long-term debt | Fannie Mae
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(307)	(382)	(373)	(416)
Total gains (losses) (realized/unrealized) Included in Net Income	54	(15)	120	19
Total gains (losses) (realized/unrealized) included in OCI	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	(253)	(397)	(253)	(397)
Net unrealized gain (losses) related to liabilities	54	(15)	120	19
Long-term debt | Consolidated Trusts
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(161)	(58)	(95)	(83)
Total gains (losses) (realized/unrealized) Included in Net Income	0	0	2	1
Total gains (losses) (realized/unrealized) included in OCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	(86)	0
Settlements	9	4	27	8
Transfers out of Level 3	0	0	1	20
Transfers into Level 3	0	(1)	(1)	(1)
Ending Balance	(152)	(55)	(152)	(55)
Net unrealized gain (losses) related to liabilities	1	0	3	0
Other Comprehensive Income (Loss) | Total trading securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to assets	0	0	0	0
Other Comprehensive Income (Loss) | Total trading securities | Fannie Mae
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to assets	0	0	0	0
Other Comprehensive Income (Loss) | Total trading securities | Other agency
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to assets				0
Other Comprehensive Income (Loss) | Total available-for-sale securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to assets	(2)	4	(5)	7
Other Comprehensive Income (Loss) | Total available-for-sale securities | Fannie Mae
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to assets	(1)	3	(3)	3
Other Comprehensive Income (Loss) | Total available-for-sale securities | Other securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to assets	(1)	1	(2)	4
Other Comprehensive Income (Loss) | Mortgage loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to assets	0	0	0	0
Other Comprehensive Income (Loss) | Net derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to assets	0	0	0	0
Other Comprehensive Income (Loss) | Long-term debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to liabilities	0	0	0	0
Other Comprehensive Income (Loss) | Long-term debt | Fannie Mae
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to liabilities	0	0	0	0
Other Comprehensive Income (Loss) | Long-term debt | Consolidated Trusts
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gain (losses) related to liabilities	$ 0	$ 0	$ 0	$ 0