Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Trading, at fair value	$ 26,630		$ 30,768
Available-for-sale, at fair value	34,026		38,171
Other assets	21,400		20,231
Other liabilities	(12,957)		(15,441)
Consolidated VIEs [Member]
Variable Interest Entities [Line Items]
Unpaid Principal Balance Previously Unconsolidated Variable Interest Entities	381
Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Unpaid Principal Balance Previously Consolidated Variable Interest Entities			316
Unconsolidated VIEs [Member] | Mortgage-Backed Trusts [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Trading, at fair value	13,348		14,219
Available-for-sale, at fair value	30,443		33,307
Other assets	118		119
Other liabilities	(1,600)		(1,668)
Net carrying amount	42,309		45,977
Maximum exposure to loss	49,596	[1]	54,148	[1]
Total assets of unconsolidated mortgage-backed trusts	284,852		313,202
Unconsolidated VIEs [Member] | Limited Partnership Investments [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Maximum exposure to loss	20		14
Total assets of unconsolidated mortgage-backed trusts	6,300		6,800
Fannie Mae Securities [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Trading, at fair value	5,514		5,660
Trading, at fair value	5,686		5,870
Available-for-sale, at fair value	5,462		5,866
Non-Fannie Mae Securities [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Trading, at fair value	7,834		8,559
Available-for-sale, at fair value	$ 24,981		$ 27,441

[1] Our maximum exposure to loss generally represents the greater of our recorded investment in the entity or the unpaid principal balance of the assets covered by our guaranty. However, our securities issued by Fannie Mae multi-class resecuritization trusts that are not consolidated do not give rise to any additional exposure to loss as we already consolidate the underlying collateral.