Allowance for Loan Losses Allowance for Loan Losses Rollforward by Segment (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended		9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014 Fannie Mae [Member]		Sep. 30, 2013 Fannie Mae [Member]		Sep. 30, 2014 Fannie Mae [Member]		Sep. 30, 2013 Fannie Mae [Member]		Sep. 30, 2014 Consolidated Trusts [Member]		Sep. 30, 2013 Consolidated Trusts [Member]		Sep. 30, 2014 Consolidated Trusts [Member]		Sep. 30, 2013 Consolidated Trusts [Member]		Sep. 30, 2014 Single-Family [Member]		Sep. 30, 2013 Single-Family [Member]		Sep. 30, 2014 Single-Family [Member]		Sep. 30, 2013 Single-Family [Member]		Sep. 30, 2014 Single-Family [Member] Fannie Mae [Member]		Sep. 30, 2013 Single-Family [Member] Fannie Mae [Member]		Sep. 30, 2014 Single-Family [Member] Fannie Mae [Member]		Sep. 30, 2013 Single-Family [Member] Fannie Mae [Member]		Sep. 30, 2014 Single-Family [Member] Consolidated Trusts [Member]		Sep. 30, 2013 Single-Family [Member] Consolidated Trusts [Member]		Sep. 30, 2014 Single-Family [Member] Consolidated Trusts [Member]		Sep. 30, 2013 Single-Family [Member] Consolidated Trusts [Member]		Sep. 30, 2014 Multifamily [Member]		Sep. 30, 2013 Multifamily [Member]		Sep. 30, 2014 Multifamily [Member]		Sep. 30, 2013 Multifamily [Member]		Sep. 30, 2014 Multifamily [Member] Fannie Mae [Member]		Sep. 30, 2013 Multifamily [Member] Fannie Mae [Member]		Sep. 30, 2014 Multifamily [Member] Fannie Mae [Member]		Sep. 30, 2013 Multifamily [Member] Fannie Mae [Member]		Sep. 30, 2014 Multifamily [Member] Consolidated Trusts [Member]		Sep. 30, 2013 Multifamily [Member] Consolidated Trusts [Member]		Sep. 30, 2014 Multifamily [Member] Consolidated Trusts [Member]		Sep. 30, 2013 Multifamily [Member] Consolidated Trusts [Member]		Sep. 30, 2014 Interest Receivable [Member]	Sep. 30, 2013 Interest Receivable [Member]	Sep. 30, 2014 Interest Receivable [Member]	Sep. 30, 2013 Interest Receivable [Member]	Sep. 30, 2014 Interest Receivable [Member] Fannie Mae [Member]	Dec. 31, 2013 Interest Receivable [Member] Fannie Mae [Member]	Sep. 30, 2014 Interest Receivable [Member] Consolidated Trusts [Member]	Dec. 31, 2013 Interest Receivable [Member] Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 39,067		$ 49,643		$ 43,846		$ 58,795		$ 36,643		$ 44,825		$ 40,521		$ 50,519		$ 2,424		$ 4,818		$ 3,325		$ 8,276		$ 38,643		$ 48,770		$ 43,307		$ 57,687		$ 36,400		$ 44,332		$ 40,202		$ 49,848		$ 2,243		$ 4,438		$ 3,105		$ 7,839		$ 424		$ 873		$ 539		$ 1,108		$ 243		$ 493		$ 319		$ 671		$ 181		$ 380		$ 220		$ 437						$ 712	$ 1,100	$ 52	$ 104
(Benefit) provision for loan losses	(1,051)	[1]	(2,600)	[1]	(3,481)	[1]	(9,033)	[1]	(1,439)	[1]	(2,150)	[1]	(3,629)	[1]	(6,811)	[1]	388	[1]	(450)	[1]	148	[1]	(2,222)	[1]	(999)	[1]	(2,471)	[1]	(3,371)	[1]	(8,738)	[1]	(1,393)	[1]	(2,126)	[1]	(3,563)	[1]	(6,660)	[1]	394	[1]	(345)	[1]	192	[1]	(2,078)	[1]	(52)	[1]	(129)	[1]	(110)	[1]	(295)	[1]	(46)	[1]	(24)	[1]	(66)	[1]	(151)	[1]	(6)	[1]	(105)	[1]	(44)	[1]	(144)	[1]
Charge-offs	(1,561)	[2],[3]	(2,325)	[2],[3]	(5,071)	[2],[3]	(7,263)	[2],[3]	(1,453)	[2],[3]	(2,275)	[2],[3]	(4,820)	[2],[3]	(7,027)	[2],[3]	(108)	[2],[3]	(50)	[2],[3]	(251)	[2],[3]	(236)	[2],[3]	(1,547)	[3]	(2,271)	[3]	(4,998)	[3]	(7,142)	[3]	(1,439)	[3]	(2,221)	[3]	(4,747)	[3]	(6,906)	[3]	(108)	[3]	(50)	[3]	(251)	[3]	(236)	[3]	(14)	[3]	(54)	[3]	(73)	[3]	(121)	[3]	(14)	[3]	(54)	[3]	(73)	[3]	(121)	[3]	0	[3]	0	[3]	0	[3]	0	[3]	(72)	(100)	(241)	(337)
Recoveries	275		294		1,124		2,138		271		257		902		1,750		4		37		222		388		275		294		1,124		2,138		271		257		902		1,750		4		37		222		388
Transfers	0	[4]	0	[4]	0	[4]	0	[4]	368	[4]	554	[4]	1,127	[4]	2,462	[4]	(368)	[4]	(554)	[4]	(1,127)	[4]	(2,462)	[4]	0	[4]	0	[4]	0	[4]	0	[4]	366	[4]	549	[4]	1,123	[4]	2,440	[4]	(366)	[4]	(549)	[4]	(1,123)	[4]	(2,440)	[4]	0	[4]	0	[4]	0	[4]	0	[4]	2	[4]	5	[4]	4	[4]	22	[4]	(2)	[4]	(5)	[4]	(4)	[4]	(22)	[4]
Other	201	[5]	157	[5]	513	[5]	532	[5]	172	[5]	134	[5]	461	[5]	452	[5]	29	[5]	23	[5]	52	[5]	80	[5]	198	[5]	154	[5]	508	[5]	531	[5]	170	[5]	132	[5]	458	[5]	451	[5]	28	[5]	22	[5]	50	[5]	80	[5]	3	[5]	3	[5]	5	[5]	1	[5]	2	[5]	2	[5]	3	[5]	1	[5]	1	[5]	1	[5]	2	[5]	0	[5]
Ending balance	36,931		45,169		36,931		45,169		34,562		41,345		34,562		41,345		2,369		3,824		2,369		3,824		36,570		44,476		36,570		44,476		34,375		40,923		34,375		40,923		2,195		3,553		2,195		3,553		361		693		361		693		187		422		187		422		174		271		174		271						712	1,100	52	104
Table Footnote [Abstract]
Charge-offs	$ 1,561	[2],[3]	$ 2,325	[2],[3]	$ 5,071	[2],[3]	$ 7,263	[2],[3]	$ 1,453	[2],[3]	$ 2,275	[2],[3]	$ 4,820	[2],[3]	$ 7,027	[2],[3]	$ 108	[2],[3]	$ 50	[2],[3]	$ 251	[2],[3]	$ 236	[2],[3]	$ 1,547	[3]	$ 2,271	[3]	$ 4,998	[3]	$ 7,142	[3]	$ 1,439	[3]	$ 2,221	[3]	$ 4,747	[3]	$ 6,906	[3]	$ 108	[3]	$ 50	[3]	$ 251	[3]	$ 236	[3]	$ 14	[3]	$ 54	[3]	$ 73	[3]	$ 121	[3]	$ 14	[3]	$ 54	[3]	$ 73	[3]	$ 121	[3]	$ 0	[3]	$ 0	[3]	$ 0	[3]	$ 0	[3]	$ 72	$ 100	$ 241	$ 337

[1] (Benefit) provision for loan losses is included in “Benefit for credit losses” in our condensed consolidated statements of operations and comprehensive income.

[2] Total charge-offs include accrued interest of $72 million and $100 million for the three months ended September 30, 2014 and 2013, respectively, and $241 million and $337 million for the nine months ended September 30, 2014 and 2013, respectively.

[3] While we purchase the substantial majority of loans that are four or more months delinquent from our MBS trusts, we do not exercise this option to purchase loans during a forbearance period. Charge-offs of consolidated trusts generally represent loans that remained in our consolidated trusts at the time of default.

[4] Includes transfers from trusts for delinquent loan purchases.

[5] Amounts represent the net activity recorded in our allowances for accrued interest receivable and preforeclosure property taxes and insurance receivable from borrowers. The (benefit) provision for loan losses, charge-offs, recoveries and transfer activity included in this table reflect all changes for both the allowance for loan losses and the valuation allowances for accrued interest and preforeclosure property taxes and insurance receivable that relate to the mortgage loans.