Fair Value Level 3 Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Trading Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 2,286	$ 2,811	$ 3,030	$ 2,774
Total gains or (losses) (realized/unrealized) Included in Net Income	51	235	66	374
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0	0	0	0
Purchases	0	0	0	0
Sales	(657)	(264)	(1,067)	(264)
Issues	0	0	0	0
Settlements	(35)	(62)	(92)	(157)
Transfers out of Level 3	0	(67)	(322)	(184)
Transfers into Level 3	0	16	30	126
Ending Balance	1,645	2,669	1,645	2,669
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	126	336	168	474
Trading Securities [Member] | Fannie Mae [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2		305	42
Total gains or (losses) (realized/unrealized) Included in Net Income	0		(27)	(1)
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0		0	0
Purchases	0		0	0
Sales	(2)		(2)	0
Issues	0		0	0
Settlements	0		0	(2)
Transfers out of Level 3	0		(278)	(39)
Transfers into Level 3	0		2	0
Ending Balance	0	0	0	0
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	0		0	0
Trading Securities [Member] | Freddie Mac [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				2
Total gains or (losses) (realized/unrealized) Included in Net Income				0
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income				0
Purchases				0
Sales				0
Issues				0
Settlements				0
Transfers out of Level 3				(2)
Transfers into Level 3				0
Ending Balance		0		0
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end				0
Trading Securities [Member] | Alt-A private-label securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	572	655	597	618
Total gains or (losses) (realized/unrealized) Included in Net Income	36	84	44	103
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0	0	0	0
Purchases	0	0	0	0
Sales	(267)	(23)	(267)	(23)
Issues	0	0	0	0
Settlements	(16)	(22)	(33)	(38)
Transfers out of Level 3	0	(67)	(44)	(143)
Transfers into Level 3	0	16	28	126
Ending Balance	325	643	325	643
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	45	84	51	101
Trading Securities [Member] | Subprime private-label securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	876	1,453	1,307	1,448
Total gains or (losses) (realized/unrealized) Included in Net Income	42	103	43	179
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0	0	0	0
Purchases	0	0	0	0
Sales	(182)	(241)	(580)	(241)
Issues	0	0	0	0
Settlements	(18)	(33)	(52)	(104)
Transfers out of Level 3	0	0	0	0
Transfers into Level 3	0	0	0	0
Ending Balance	718	1,282	718	1,282
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	97	204	99	280
Trading Securities [Member] | Mortgage revenue bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	742	601	722	565
Total gains or (losses) (realized/unrealized) Included in Net Income	(33)	44	2	84
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0	0	0	0
Purchases	0	0	0	0
Sales	(106)	0	(118)	0
Issues	0	0	0	0
Settlements	(1)	(2)	(4)	(6)
Transfers out of Level 3	0	0	0	0
Transfers into Level 3	0	0	0	0
Ending Balance	602	643	602	643
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	(36)	44	(1)	84
Trading Securities [Member] | Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	94	102	99	99
Total gains or (losses) (realized/unrealized) Included in Net Income	6	4	4	9
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0	0	0	0
Purchases	0	0	0	0
Sales	(100)	0	(100)	0
Issues	0	0	0	0
Settlements	0	(5)	(3)	(7)
Transfers out of Level 3	0	0	0	0
Transfers into Level 3	0	0	0	0
Ending Balance	0	101	0	101
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	20	4	19	9
Available-for-sale securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	13,471	18,463	15,080	19,012
Total gains or (losses) (realized/unrealized) Included in Net Income	398	367	564	396
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	(303)	79	(290)	605
Purchases	182	0	421	0
Sales	(2,103)	(1,708)	(3,420)	(1,727)
Issues	0	0	0	0
Settlements	(475)	(889)	(1,187)	(1,753)
Transfers out of Level 3	(228)	(269)	(539)	(880)
Transfers into Level 3	11	767	324	1,157
Ending Balance	10,953	16,810	10,953	16,810
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	0	0	0	0
Available-for-sale securities [Member] | Fannie Mae [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	205	5	0	7
Total gains or (losses) (realized/unrealized) Included in Net Income	0	0	0	0
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0	0	0	0
Purchases	182	0	421	0
Sales	(269)	0	(303)	0
Issues	0	0	0	0
Settlements	0	(1)	0	(1)
Transfers out of Level 3	0	(4)	0	(6)
Transfers into Level 3	11	2	11	2
Ending Balance	129	2	129	2
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	0	0	0	0
Available-for-sale securities [Member] | Freddie Mac [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	5	8	6	8
Total gains or (losses) (realized/unrealized) Included in Net Income	0	0	0	0
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(1)	0	(1)	0
Transfers out of Level 3	0	0	(1)	0
Transfers into Level 3	0	1	0	1
Ending Balance	4	9	4	9
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	0	0	0	0
Available-for-sale securities [Member] | Alt-A private-label securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,486	3,570	3,140	3,791
Total gains or (losses) (realized/unrealized) Included in Net Income	71	103	172	116
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	(38)	(24)	(116)	49
Purchases	0	0	0	0
Sales	(552)	(320)	(1,108)	(320)
Issues	0	0	0	0
Settlements	(85)	(111)	(209)	(199)
Transfers out of Level 3	(228)	(265)	(538)	(874)
Transfers into Level 3	0	764	313	1,154
Ending Balance	1,654	3,717	1,654	3,717
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	0	0	0	0
Available-for-sale securities [Member] | Subprime private-label securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	4,608	7,030	5,240	7,068
Total gains or (losses) (realized/unrealized) Included in Net Income	265	268	445	301
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	(131)	(38)	(232)	181
Purchases	0	0	0	0
Sales	(760)	(1,349)	(1,325)	(1,349)
Issues	0	0	0	0
Settlements	(145)	(206)	(291)	(496)
Transfers out of Level 3	0	0	0	0
Transfers into Level 3	0	0	0	0
Ending Balance	3,837	5,705	3,837	5,705
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	0	0	0	0
Available-for-sale securities [Member] | Mortgage revenue bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,560	5,006	4,023	5,253
Total gains or (losses) (realized/unrealized) Included in Net Income	17	(7)	40	(27)
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	(79)	87	(27)	280
Purchases	0	0	0	0
Sales	(154)	(39)	(316)	(58)
Issues	0	0	0	0
Settlements	(173)	(487)	(549)	(888)
Transfers out of Level 3	0	0	0	0
Transfers into Level 3	0	0	0	0
Ending Balance	3,171	4,560	3,171	4,560
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	0	0	0	0
Available-for-sale securities [Member] | Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,607	2,844	2,671	2,885
Total gains or (losses) (realized/unrealized) Included in Net Income	45	3	(93)	6
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	(55)	54	85	95
Purchases	0	0	0	0
Sales	(368)	0	(368)	0
Issues	0	0	0	0
Settlements	(71)	(84)	(137)	(169)
Transfers out of Level 3	0	0	0	0
Transfers into Level 3	0	0	0	0
Ending Balance	2,158	2,817	2,158	2,817
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	0	0	0	0
Mortgage Loans [Member] | Consolidated Trusts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,810	2,608	1,833	2,704
Total gains or (losses) (realized/unrealized) Included in Net Income	4	102	38	127
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0	0	0	0
Purchases	2	7	5	31
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(99)	(85)	(176)	(166)
Transfers out of Level 3	(197)	(165)	(254)	(313)
Transfers into Level 3	75	64	149	148
Ending Balance	1,595	2,531	1,595	2,531
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	(6)	86	5	94
Net derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	66	(23)	45	(40)
Total gains or (losses) (realized/unrealized) Included in Net Income	(126)	47	(99)	77
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	64	(4)	58	(16)
Transfers out of Level 3	0	0	0	(1)
Transfers into Level 3	0	0	0	0
Ending Balance	4	20	4	20
Net unrealized gains (losses) included in net income related to assets and liabilities still held at period end	(40)	41	(23)	54
Long-term debt [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(938)	(816)	(890)	(1,473)
Total (Losses) Gains (Realized/Unrealized) Included in Net Loss	50	(48)	9	(139)
Total Gains or (Losses) Included in Other Comprehensive Income (Loss)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	(1)	0	(751)
Settlements	16	17	25	55
Transfers out of Level 3	59	47	109	1,531
Transfers into Level 3	(26)	(22)	(92)	(46)
Ending Balance	(839)	(823)	(839)	(823)
Net Unrealized Gain (Loss) Included in Net Loss Related to Liabilities Still Held at period end	52	(46)	12	(91)
Long-term debt [Member] | Consolidated Trusts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(547)	(506)	(527)	(518)
Total (Losses) Gains (Realized/Unrealized) Included in Net Loss	5	(33)	(8)	(34)
Total Gains or (Losses) Included in Other Comprehensive Income (Loss)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	(1)	0	(1)
Settlements	16	17	25	35
Transfers out of Level 3	59	47	109	66
Transfers into Level 3	(26)	(22)	(92)	(46)
Ending Balance	(493)	(498)	(493)	(498)
Net Unrealized Gain (Loss) Included in Net Loss Related to Liabilities Still Held at period end	8	(31)	(4)	(32)
Long-term debt [Member] | Senior Floating [Member] | Fannie Mae [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(391)	(310)	(363)	(955)
Total (Losses) Gains (Realized/Unrealized) Included in Net Loss	45	(15)	17	(105)
Total Gains or (Losses) Included in Other Comprehensive Income (Loss)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	(750)
Settlements	0	0	0	20
Transfers out of Level 3	0	0	0	1,465
Transfers into Level 3	0	0	0	0
Ending Balance	(346)	(325)	(346)	(325)
Net Unrealized Gain (Loss) Included in Net Loss Related to Liabilities Still Held at period end	$ 44	$ (15)	$ 16	$ (59)