Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Available-for-sale, at fair value	$ 41,000		$ 63,181
Trading, at fair value	32,860		40,695
Other assets	23,241		27,939
Other liabilities	(18,715)		(14,378)
Unconsolidated VIEs [Member] | Mortgage-Backed Trusts [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Available-for-sale, at fair value	36,653	[1]	57,004	[1]
Trading, at fair value	16,431	[1]	22,706	[1]
Other assets	115		145
Other liabilities	(1,408)		(1,449)
Net carrying amount	51,791		78,406
Maximum exposure to loss	58,934	[1],[2]	87,397	[1],[2]
Total assets of unconsolidated VIEs	367,866	[1]	645,332	[1]
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	21		118
Total assets of unconsolidated VIEs	7,000		11,700
Fannie Mae Securities [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Available-for-sale, at fair value	7,199	[1]	10,435	[1]
Trading, at fair value	6,081	[1]	6,248	[1]
Non-Fannie Mae Securities [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Available-for-sale, at fair value	29,454	[1]	46,569	[1]
Trading, at fair value	$ 10,350	[1]	$ 16,458	[1]

[1] Contains securities recognized in our condensed consolidated balance sheets due to consolidation of certain multi-class resecuritization trusts.

[2] 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.