Fair Value FV Measurement 2 - Level 3 Reconciliation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	$ 245		$ 108
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	202		17
Interest Income [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	55		66
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0		0
Fair Value Gains (Losses), Net [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	192		87
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	202		17
Net Other-than-Temporary Impairments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	(5)		(51)
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0		0
Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	3		6
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0		0
Trading securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,286		4,238
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	240		4
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	(33)	[2]
Issues	0	[3]	0	[3]
Settlements	(55)	[3]	(158)	[3]
Transfers out of Level 3	(44)	[4]	(1,590)	[4]
Transfers Into Level 3	325	[4]	295	[4]
Ending Balance	2,752		2,756
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	236	[5]	(2)	[5]
Trading securities [Member] | Fannie Mae [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	68		1,737
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	(3)		5
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	(33)	[2]
Issues	0	[3]	0	[3]
Settlements	(4)	[3]	(104)	[3]
Transfers out of Level 3	0	[4]	(1,581)	[4]
Transfers Into Level 3	0	[4]	65	[4]
Ending Balance	61		89
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	(2)	[5]	0	[5]
Trading securities [Member] | Freddie Mac [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2		0
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	0		0
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	0	[3]	0	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	0	[4]	2	[4]
Ending Balance	2		2
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0	[5]	0	[5]
Trading securities [Member] | Ginnie Mae [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1		9
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	0		0
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(1)	[3]	0	[3]
Transfers out of Level 3	0	[4]	(9)	[4]
Transfers Into Level 3	0	[4]	0	[4]
Ending Balance	0		0
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0	[5]	0	[5]
Trading securities [Member] | Alt-A private-label securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	104		345
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	95		13
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(16)	[3]	(17)	[3]
Transfers out of Level 3	(44)	[4]	0	[4]
Transfers Into Level 3	325	[4]	228	[4]
Ending Balance	464		569
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	90	[5]	13	[5]
Trading securities [Member] | Subprime private-label securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,319		1,280
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	159		59
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(32)	[3]	(34)	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	0	[4]	0	[4]
Ending Balance	1,446		1,305
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	160	[5]	59	[5]
Trading securities [Member] | Mortgage revenue bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	675		724
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	(13)		(54)
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(1)	[3]	(2)	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	0	[4]	0	[4]
Ending Balance	661		668
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	(13)	[5]	(55)	[5]
Trading securities [Member] | Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	117		143
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	2		(19)
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(1)	[3]	(1)	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	0	[4]	0	[4]
Ending Balance	118		123
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	1	[5]	(19)	[5]
Available-for-sale securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	25,034		29,492
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	55		26
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	910	[1]	298	[1]
Purchases	0	[2]	1	[2]
Sales	(19)	[2]	(25)	[2]
Issues	0	[3]	0	[3]
Settlements	(1,104)	[3]	(1,047)	[3]
Transfers out of Level 3	(1,206)	[4]	(1,880)	[4]
Transfers Into Level 3	781	[4]	988	[4]
Ending Balance	24,451		27,853
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0	[5]	0	[5]
Available-for-sale securities [Member] | Fannie Mae [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	29		946
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	0		0
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	(8)	[1]
Purchases	0	[2]	1	[2]
Sales	0	[2]	(1)	[2]
Issues	0	[3]	0	[3]
Settlements	(3)	[3]	(16)	[3]
Transfers out of Level 3	(14)	[4]	(895)	[4]
Transfers Into Level 3	0	[4]	10	[4]
Ending Balance	12		37
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0	[5]	0	[5]
Available-for-sale securities [Member] | Freddie Mac [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	10		12
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	0		0
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(1)	[3]	(1)	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	0	[4]	0	[4]
Ending Balance	9		11
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0	[5]	0	[5]
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	6,564		7,256
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	9		(17)
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	218	[1]	166	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(268)	[3]	(262)	[3]
Transfers out of Level 3	(1,192)	[4]	(985)	[4]
Transfers Into Level 3	781	[4]	978	[4]
Ending Balance	6,112		7,136
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0	[5]	0	[5]
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	7,447		7,586
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	44		35
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	677	[1]	303	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(300)	[3]	(329)	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	0	[4]	0	[4]
Ending Balance	7,868		7,595
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0	[5]	0	[5]
Available-for-sale securities [Member] | Mortgage revenue bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	7,837		10,247
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	(2)		2
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	(29)	[1]	(137)	[1]
Purchases	0	[2]	0	[2]
Sales	(19)	[2]	(24)	[2]
Issues	0	[3]	0	[3]
Settlements	(436)	[3]	(356)	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	0	[4]	0	[4]
Ending Balance	7,351		9,732
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0	[5]	0	[5]
Available-for-sale securities [Member] | Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,147		3,445
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	4		6
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	44	[1]	(26)	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(96)	[3]	(83)	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	0	[4]	0	[4]
Ending Balance	3,099		3,342
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	0	[5]	0	[5]
Mortgage Loans [Member] | Consolidated Trusts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,634		2,319
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	27		73
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	158	[2]	245	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	(112)	[3]	(59)	[3]
Transfers out of Level 3	(38)	[4]	(318)	[4]
Transfers Into Level 3	213	[4]	11	[4]
Ending Balance	2,882		2,271
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	22	[5]	17	[5]
Net derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	14		65
Total Gains or (Losses) (Realized/Unrealized) Included in Net Income (Loss)	(40)		7
Total Gains or (Losses) (Realized/Unrealized) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	(3)	[3]
Settlements	23	[3]	(25)	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	(4)	[4]	0	[4]
Ending Balance	(7)		44
Net Unrealized Gains (Losses) Included in Net Income (Loss) Related to Assets Still Held	(18)	[5]	3	[5]
Long-term debt [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(1,528)		(1,171)
Total Gains (Losses) (Realized/Unrealized) Included in Net Loss	(37)		(2)
Total Gains or (Losses) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	(15)	[3]	(267)	[3]
Settlements	49	[3]	28	[3]
Transfers out of Level 3	113	[4]	110	[4]
Transfers Into Level 3	(42)	[4]	(47)	[4]
Ending Balance	(1,460)		(1,349)
Net Unrealized Gain (Loss) Included in Net Loss Related to Liabilities Still Held	(38)	[5]	(1)	[5]
Long-term debt [Member] | Consolidated Trusts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(1,128)		(765)
Total Gains (Losses) (Realized/Unrealized) Included in Net Loss	(54)		(9)
Total Gains or (Losses) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	(15)	[3]	(267)	[3]
Settlements	49	[3]	28	[3]
Transfers out of Level 3	113	[4]	110	[4]
Transfers Into Level 3	(42)	[4]	(47)	[4]
Ending Balance	(1,077)		(950)
Net Unrealized Gain (Loss) Included in Net Loss Related to Liabilities Still Held	(55)	[5]	(8)	[5]
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	(400)		(406)
Total Gains (Losses) (Realized/Unrealized) Included in Net Loss	17		7
Total Gains or (Losses) Included in Other Comprehensive Income (Loss)	0	[1]	0	[1]
Purchases	0	[2]	0	[2]
Sales	0	[2]	0	[2]
Issues	0	[3]	0	[3]
Settlements	0	[3]	0	[3]
Transfers out of Level 3	0	[4]	0	[4]
Transfers Into Level 3	0	[4]	0	[4]
Ending Balance	(383)		(399)
Net Unrealized Gain (Loss) Included in Net Loss Related to Liabilities Still Held	$ 17	[5]	$ 7	[5]

[1] Gains (losses) included in other comprehensive income are included in “Changes in unrealized gains on available-for-sale securities, net of reclassification adjustments and taxes” in the condensed consolidated statements of operations and comprehensive income.

[2] Purchases and sales include activity related to the consolidation and deconsolidation of assets of securitization trusts.

[3] Issues and settlements include activity related to the consolidation and deconsolidation of liabilities of securitization trusts.

[4] Transfers out of Level 3 consisted primarily of Fannie Mae MBS and private-label mortgage-related securities backed by Alt-A loans. Prices for these securities were obtained from multiple third-party vendors supported by market observable inputs. Transfers into Level 3 consisted primarily of private-label mortgage-related securities backed by Alt-A loans. Prices for these securities are based on inputs from a single source or inputs that were not readily observable.

[5] Amount represents temporary changes in fair value. Amortization, accretion and other-than-temporary impairments are not considered unrealized and are not included in this amount.