Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 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	$ 60,329		$ 63,181
Trading, at fair value	52,391		40,695
Other assets	20,278		27,939
Other liabilities	(14,383)		(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	54,616	[1]	57,004	[1]
Trading, at fair value	23,947	[1]	22,706	[1]
Other assets	137		145
Other liabilities	(1,436)		(1,449)
Net carrying amount	77,264		78,406
Maximum exposure to loss	85,533	[1],[2]	87,397	[1],[2]
Total assets of unconsolidated VIEs	585,532	[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	113	[1]	118	[1]
Total assets of unconsolidated VIEs	$ 11,600	[1]	$ 11,700	[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.