Fair Value Levels Hierarchy (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Other assets [Abstract]
Derivative assets, gross amount offset	$ (4,050)	$ (5,186)
Other liabilities [Abstract]
Derivative liabilities, gross amount offset	(7,728)	(10,194)
Mortgage commitment derivatives [Member]
Other assets [Abstract]
Derivative assets, gross amount offset	0	0
Other liabilities [Abstract]
Derivative liabilities, gross amount offset	0	0
Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	8,861	6,403
Consolidated Trusts [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	14,981	15,629
Liabilities [Abstract]
Long-term debt, fair value	22,885	19,483
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets [Abstract]
Trading Securities	23,790	19,466
Available-for-sale securities	0	0
Mortgage loans held for investment, at fair value	0	0
Total assets at fair value	65,341	57,431
Other assets [Abstract]
Derivatives assets at fair value	0	0
Liabilities [Abstract]
Total liabilities at fair value	0	0
Other liabilities [Abstract]
Derivative liabilities at fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fannie Mae [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	0	0
Liabilities [Abstract]
Long-term debt, fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Consolidated Trusts [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	0	0
Liabilities [Abstract]
Long-term debt, fair value	0	0
Significant Other Observable Inputs (Level 2) [Member]
Assets [Abstract]
Trading Securities	9,429	9,008
Available-for-sale securities	13,208	15,574
Mortgage loans held for investment, at fair value	2,676,066	2,687,759
Total assets at fair value	2,746,853	2,771,628
Other assets [Abstract]
Derivatives assets at fair value	5,619	6,489
Liabilities [Abstract]
Total liabilities at fair value	3,240,390	3,299,289
Other liabilities [Abstract]
Derivative liabilities at fair value	8,394	10,671
Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	28,165	29,896
Liabilities [Abstract]
Long-term debt, fair value	354,566	367,703
Significant Other Observable Inputs (Level 2) [Member] | Consolidated Trusts [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	2,647,901	2,657,863
Liabilities [Abstract]
Long-term debt, fair value	2,796,069	2,815,843
Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Trading Securities	1,645	3,030
Available-for-sale securities	10,953	15,080
Mortgage loans held for investment, at fair value	381,870	400,327
Total assets at fair value	400,252	419,874
Other assets [Abstract]
Derivatives assets at fair value	149	182
Liabilities [Abstract]
Total liabilities at fair value	26,979	23,592
Other liabilities [Abstract]
Derivative liabilities at fair value	145	137
Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	207,356	217,064
Liabilities [Abstract]
Long-term debt, fair value	955	982
Significant Unobservable Inputs (Level 3) [Member] | Consolidated Trusts [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	174,514	183,263
Liabilities [Abstract]
Long-term debt, fair value	23,138	19,334
Recurring Fair Value Measurements [Member]
Assets [Abstract]
Trading Securities	34,864	31,504
Available-for-sale securities	24,161	30,654
Total assets at fair value	75,724	79,272
Other assets [Abstract]
Derivatives assets at fair value	1,718	1,485
Derivative assets, gross amount offset	(4,050)	(5,186)
Liabilities [Abstract]
Long-term debt, fair value	31,746	25,886
Total liabilities at fair value	32,557	26,500
Other liabilities [Abstract]
Derivative liabilities at fair value	811	614
Derivative liabilities, gross amount offset	(7,728)	(10,194)
Recurring Fair Value Measurements [Member] | Swaps [Member]
Other assets [Abstract]
Derivatives assets at fair value	5,256	6,235
Other liabilities [Abstract]
Derivative liabilities at fair value	7,812	9,472
Recurring Fair Value Measurements [Member] | Swaptions [Member]
Other assets [Abstract]
Derivatives assets at fair value	53	153
Other liabilities [Abstract]
Derivative liabilities at fair value	334	991
Recurring Fair Value Measurements [Member] | Other [Member]
Other assets [Abstract]
Derivatives assets at fair value	26	28
Other liabilities [Abstract]
Derivative liabilities at fair value	1	1
Recurring Fair Value Measurements [Member] | Mortgage commitment derivatives [Member]
Other assets [Abstract]
Derivatives assets at fair value	433	255
Other liabilities [Abstract]
Derivative liabilities at fair value	392	344
Recurring Fair Value Measurements [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	8,861	6,403
Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Senior Floating [Member]
Liabilities [Abstract]
Long-term debt, fair value	8,861	6,403
Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	14,981	15,629
Liabilities [Abstract]
Long-term debt, fair value	22,885	19,483
Recurring Fair Value Measurements [Member] | Fannie Mae [Member]
Assets [Abstract]
Trading Securities	5,079	4,940
Available-for-sale securities	4,638	5,639
Recurring Fair Value Measurements [Member] | Freddie Mac [Member]
Assets [Abstract]
Trading Securities	1,537	1,369
Available-for-sale securities	4,947	5,528
Recurring Fair Value Measurements [Member] | Ginnie Mae [Member]
Assets [Abstract]
Trading Securities	239	166
Available-for-sale securities	435	476
Recurring Fair Value Measurements [Member] | Alt-A private-label securities [Member]
Assets [Abstract]
Trading Securities	475	920
Available-for-sale securities	3,630	5,678
Recurring Fair Value Measurements [Member] | Subprime private-label securities [Member]
Assets [Abstract]
Trading Securities	718	1,307
Available-for-sale securities	3,837	5,240
Recurring Fair Value Measurements [Member] | CMBS [Member]
Assets [Abstract]
Trading Securities	2,424	2,515
Available-for-sale securities	1,344	1,397
Recurring Fair Value Measurements [Member] | Mortgage revenue bonds [Member]
Assets [Abstract]
Trading Securities	602	722
Available-for-sale securities	3,171	4,023
Recurring Fair Value Measurements [Member] | Other [Member]
Assets [Abstract]
Trading Securities		99
Available-for-sale securities	2,159	2,673
Recurring Fair Value Measurements [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Trading Securities	23,790	19,466
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets [Abstract]
Trading Securities	23,790	19,466
Available-for-sale securities	0	0
Total assets at fair value	23,790	19,466
Other assets [Abstract]
Derivatives assets at fair value	0	0
Liabilities [Abstract]
Long-term debt, fair value	0	0
Total liabilities at fair value	0	0
Other liabilities [Abstract]
Derivative liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Swaps [Member]
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivative liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Swaptions [Member]
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivative liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other [Member]
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivative liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage commitment derivatives [Member]
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivative liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fannie Mae [Member] | Senior Floating [Member]
Liabilities [Abstract]
Long-term debt, fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Consolidated Trusts [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	0	0
Liabilities [Abstract]
Long-term debt, fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fannie Mae [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Freddie Mac [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Ginnie Mae [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Alt-A private-label securities [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Subprime private-label securities [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | CMBS [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage revenue bonds [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other [Member]
Assets [Abstract]
Trading Securities		0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Trading Securities	23,790	19,466
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets [Abstract]
Trading Securities	9,429	9,008
Available-for-sale securities	13,208	15,574
Total assets at fair value	41,642	44,867
Other assets [Abstract]
Derivatives assets at fair value	5,619	6,489
Liabilities [Abstract]
Long-term debt, fair value	30,907	24,996
Total liabilities at fair value	39,301	35,667
Other liabilities [Abstract]
Derivative liabilities at fair value	8,394	10,671
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Swaps [Member]
Other assets [Abstract]
Derivatives assets at fair value	5,134	6,085
Other liabilities [Abstract]
Derivative liabilities at fair value	7,692	9,339
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Swaptions [Member]
Other assets [Abstract]
Derivatives assets at fair value	53	153
Other liabilities [Abstract]
Derivative liabilities at fair value	334	991
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other [Member]
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivative liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage commitment derivatives [Member]
Other assets [Abstract]
Derivatives assets at fair value	432	251
Other liabilities [Abstract]
Derivative liabilities at fair value	368	341
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	8,515	6,040
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member] | Senior Floating [Member]
Liabilities [Abstract]
Long-term debt, fair value	8,515	6,040
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Consolidated Trusts [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	13,386	13,796
Liabilities [Abstract]
Long-term debt, fair value	22,392	18,956
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member]
Assets [Abstract]
Trading Securities	5,079	4,635
Available-for-sale securities	4,509	5,639
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Freddie Mac [Member]
Assets [Abstract]
Trading Securities	1,537	1,369
Available-for-sale securities	4,943	5,522
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Ginnie Mae [Member]
Assets [Abstract]
Trading Securities	239	166
Available-for-sale securities	435	476
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Alt-A private-label securities [Member]
Assets [Abstract]
Trading Securities	150	323
Available-for-sale securities	1,976	2,538
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Subprime private-label securities [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | CMBS [Member]
Assets [Abstract]
Trading Securities	2,424	2,515
Available-for-sale securities	1,344	1,397
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage revenue bonds [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other [Member]
Assets [Abstract]
Trading Securities		0
Available-for-sale securities	1	2
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Trading Securities	0	0
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Trading Securities	1,645	3,030
Available-for-sale securities	10,953	15,080
Total assets at fair value	14,342	20,125
Other assets [Abstract]
Derivatives assets at fair value	149	182
Liabilities [Abstract]
Long-term debt, fair value	839	890
Total liabilities at fair value	984	1,027
Other liabilities [Abstract]
Derivative liabilities at fair value	145	137
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Swaps [Member]
Other assets [Abstract]
Derivatives assets at fair value	122	150
Other liabilities [Abstract]
Derivative liabilities at fair value	120	133
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Swaptions [Member]
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivative liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other [Member]
Other assets [Abstract]
Derivatives assets at fair value	26	28
Other liabilities [Abstract]
Derivative liabilities at fair value	1	1
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage commitment derivatives [Member]
Other assets [Abstract]
Derivatives assets at fair value	1	4
Other liabilities [Abstract]
Derivative liabilities at fair value	24	3
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	346	363
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member] | Senior Floating [Member]
Liabilities [Abstract]
Long-term debt, fair value	346	363
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Consolidated Trusts [Member]
Assets [Abstract]
Mortgage loans held for investment, at fair value	1,595	1,833
Liabilities [Abstract]
Long-term debt, fair value	493	527
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]
Assets [Abstract]
Trading Securities	0	305
Available-for-sale securities	129	0
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Freddie Mac [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	4	6
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Ginnie Mae [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Alt-A private-label securities [Member]
Assets [Abstract]
Trading Securities	325	597
Available-for-sale securities	1,654	3,140
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Subprime private-label securities [Member]
Assets [Abstract]
Trading Securities	718	1,307
Available-for-sale securities	3,837	5,240
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | CMBS [Member]
Assets [Abstract]
Trading Securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage revenue bonds [Member]
Assets [Abstract]
Trading Securities	602	722
Available-for-sale securities	3,171	4,023
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other [Member]
Assets [Abstract]
Trading Securities		99
Available-for-sale securities	2,158	2,671
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Trading Securities	$ 0	$ 0