Fair Value Level 3 Reconciliation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Trading securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 2,774	$ 2,286	$ 4,238
Total (Losses) or Gains (Realized/Unrealized) included in net income	512	469	307
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	0	0
Purchases	6	0	0
Sales	(299)	(50)	(33)
Issues	0	0	0
Settlements	(277)	(304)	(409)
Transfers out of Level 3	(267)	(438)	(2,497)
Transfers Into Level 3	581	811	680
Ending Balance	3,030	2,774	2,286
Net Unrealized (Losses) Gains included in net income related to assets still held	486	430	177
Trading securities [Member] | Fannie Mae [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	42	68	1,737
Total (Losses) or Gains (Realized/Unrealized) included in net income	(27)	(9)	(2)
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	0	0
Purchases	6	0	0
Sales	0	0	(33)
Issues	0	0	0
Settlements	(2)	(17)	(118)
Transfers out of Level 3	(39)	0	(1,581)
Transfers Into Level 3	325	0	65
Ending Balance	305	42	68
Net Unrealized (Losses) Gains included in net income related to assets still held	(18)	(9)	(6)
Trading securities [Member] | Freddie Mac [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	2	0
Total (Losses) or Gains (Realized/Unrealized) included in net income	0	0	0
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	0
Settlements	0	0	0
Transfers out of Level 3	(2)	0	0
Transfers Into Level 3	0	0	2
Ending Balance	0	2	2
Net Unrealized (Losses) Gains included in net income related to assets still held	0	0	0
Trading securities [Member] | Ginnie Mae [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		1	9
Total (Losses) or Gains (Realized/Unrealized) included in net income		0	0
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income		0	0
Purchases		0	0
Sales		0	0
Issues		0	0
Settlements		(1)	0
Transfers out of Level 3		(3)	(9)
Transfers Into Level 3		3	1
Ending Balance		0	1
Net Unrealized (Losses) Gains included in net income related to assets still held		0	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	618	104	345
Total (Losses) or Gains (Realized/Unrealized) included in net income	88	256	165
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	0	0
Purchases	0	0	0
Sales	(58)	0	0
Issues	0	0	0
Settlements	(81)	(115)	(111)
Transfers out of Level 3	(226)	(435)	(907)
Transfers Into Level 3	256	808	612
Ending Balance	597	618	104
Net Unrealized (Losses) Gains included in net income related to assets still held	97	223	39
Trading securities [Member] | Subprime private-label securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,448	1,319	1,280
Total (Losses) or Gains (Realized/Unrealized) included in net income	270	328	192
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	0	0
Purchases	0	0	0
Sales	(241)	(50)	0
Issues	0	0	0
Settlements	(170)	(149)	(153)
Transfers out of Level 3	0	0	0
Transfers Into Level 3	0	0	0
Ending Balance	1,307	1,448	1,319
Net Unrealized (Losses) Gains included in net income related to assets still held	234	322	192
Trading securities [Member] | Mortgage revenue bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	565	675	724
Total (Losses) or Gains (Realized/Unrealized) included in net income	168	(101)	(29)
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	0
Settlements	(11)	(9)	(20)
Transfers out of Level 3	0	0	0
Transfers Into Level 3	0	0	0
Ending Balance	722	565	675
Net Unrealized (Losses) Gains included in net income related to assets still held	160	(101)	(29)
Trading securities [Member] | Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	99	117	143
Total (Losses) or Gains (Realized/Unrealized) included in net income	13	(5)	(19)
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	0
Settlements	(13)	(13)	(7)
Transfers out of Level 3	0	0	0
Transfers Into Level 3	0	0	0
Ending Balance	99	99	117
Net Unrealized (Losses) Gains included in net income related to assets still held	13	(5)	(19)
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	19,012	25,034	29,492
Total (Losses) or Gains (Realized/Unrealized) included in net income	606	302	(192)
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	932	1,665	1,892
Purchases	0	359	72
Sales	(2,193)	(4,016)	(119)
Issues	0	0	0
Settlements	(3,337)	(4,642)	(5,109)
Transfers out of Level 3	(1,748)	(3,373)	(4,220)
Transfers Into Level 3	1,808	3,683	3,218
Ending Balance	15,080	19,012	25,034
Net Unrealized (Losses) Gains included in net income related to assets still held	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	7	29	946
Total (Losses) or Gains (Realized/Unrealized) included in net income	0	0	0
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	(1)	(8)
Purchases	0	0	43
Sales	0	0	(43)
Issues	0	0	0
Settlements	(1)	(7)	(24)
Transfers out of Level 3	(8)	(14)	(895)
Transfers Into Level 3	2	0	10
Ending Balance	0	7	29
Net Unrealized (Losses) Gains included in net income related to assets still held	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	8	10	12
Total (Losses) or Gains (Realized/Unrealized) included in net income	0	0	0
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	(1)	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	0
Settlements	(1)	(2)	(2)
Transfers out of Level 3	(2)	(1)	0
Transfers Into Level 3	1	2	0
Ending Balance	6	8	10
Net Unrealized (Losses) Gains included in net income related to assets still held	0	0	0
Available-for-sale Securities [Member] | Ginnie Mae [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		0
Total (Losses) or Gains (Realized/Unrealized) included in net income		0
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income		0
Purchases		0
Sales		0
Issues		0
Settlements		0
Transfers out of Level 3		(1)
Transfers Into Level 3		1
Ending Balance		0
Net Unrealized (Losses) Gains included in net income related to assets still held		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	3,791	6,564	7,256
Total (Losses) or Gains (Realized/Unrealized) included in net income	172	144	(87)
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	(26)	464	584
Purchases	0	0	0
Sales	(393)	(2,664)	0
Issues	0	0	0
Settlements	(471)	(1,040)	(1,072)
Transfers out of Level 3	(1,738)	(3,357)	(3,325)
Transfers Into Level 3	1,805	3,680	3,208
Ending Balance	3,140	3,791	6,564
Net Unrealized (Losses) Gains included in net income related to assets still held	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	7,068	7,447	7,586
Total (Losses) or Gains (Realized/Unrealized) included in net income	447	120	(126)
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	301	1,527	1,280
Purchases	0	359	0
Sales	(1,730)	(1,317)	0
Issues	0	0	0
Settlements	(846)	(1,068)	(1,293)
Transfers out of Level 3	0	0	0
Transfers Into Level 3	0	0	0
Ending Balance	5,240	7,068	7,447
Net Unrealized (Losses) Gains included in net income related to assets still held	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	5,253	7,837	10,247
Total (Losses) or Gains (Realized/Unrealized) included in net income	(32)	25	9
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	554	(449)	(23)
Purchases	0	0	29
Sales	(70)	(35)	(76)
Issues	0	0	0
Settlements	(1,682)	(2,125)	(2,349)
Transfers out of Level 3	0	0	0
Transfers Into Level 3	0	0	0
Ending Balance	4,023	5,253	7,837
Net Unrealized (Losses) Gains included in net income related to assets still held	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	2,885	3,147	3,445
Total (Losses) or Gains (Realized/Unrealized) included in net income	19	13	12
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	103	125	59
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	0
Settlements	(336)	(400)	(369)
Transfers out of Level 3	0	0	0
Transfers Into Level 3	0	0	0
Ending Balance	2,671	2,885	3,147
Net Unrealized (Losses) Gains included in net income related to assets still held	0	0	0
Mortgage Loans [Member] | Consolidated Trusts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,704	2,634	2,319
Total (Losses) or Gains (Realized/Unrealized) included in net income	260	282	235
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	0	0
Purchases	36	346	935
Sales	0	(393)	0
Issues	0	0	0
Settlements	(344)	(459)	(411)
Transfers out of Level 3	(1,113)	(352)	(562)
Transfers Into Level 3	290	646	118
Ending Balance	1,833	2,704	2,634
Net Unrealized (Losses) Gains included in net income related to assets still held	53	50	159
Net derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(40)	14	65
Total (Losses) or Gains (Realized/Unrealized) included in net income	103	(165)	(23)
Total (Losses) or Gains (realized/unrealized) included in other comprehensive income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	(8)
Settlements	(21)	97	(20)
Transfers out of Level 3	(2)	16	0
Transfers Into Level 3	5	(2)	0
Ending Balance	45	(40)	14
Net Unrealized (Losses) Gains included in net income related to assets still held	77	(51)	(9)
Long-term Debt [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(1,473)	(1,528)	(1,171)
Total (Losses) or Gains (realized/unrealized) included in net income	(195)	(174)	(201)
Total (Losses) or Gains included in other comprehensive income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issuances	(751)	(695)	(523)
Settlements	81	580	260
Transfers out of Level 3	1,576	434	474
Transfers Into Level 3	(128)	(90)	(367)
Ending Balance	(890)	(1,473)	(1,528)
Net unrealized (Losses) Gains included in net income related to Liabilities still held	(146)	(4)	(179)
Long-term Debt [Member] | Consolidated Trusts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(518)	(1,128)	(765)
Total (Losses) or Gains (realized/unrealized) included in net income	(53)	(250)	(180)
Total (Losses) or Gains included in other comprehensive income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issuances	(1)	(21)	(523)
Settlements	62	537	233
Transfers out of Level 3	111	434	474
Transfers Into Level 3	(128)	(90)	(367)
Ending Balance	(527)	(518)	(1,128)
Net unrealized (Losses) Gains included in net income related to Liabilities still held	(49)	(80)	(158)
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	(955)	(400)	(406)
Total (Losses) or Gains (realized/unrealized) included in net income	(142)	76	(21)
Total (Losses) or Gains included in other comprehensive income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issuances	(750)	(674)	0
Settlements	19	43	27
Transfers out of Level 3	1,465	0	0
Transfers Into Level 3	0	0	0
Ending Balance	(363)	(955)	(400)
Net unrealized (Losses) Gains included in net income related to Liabilities still held	$ (97)	$ 76	$ (21)