Fair Value Nonrecurring Changes - Prior to Adoption (Details) (Fair Value, Measurements, Nonrecurring [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total gains (losses) on mortgage loans held for sale	$ 12		$ (91)	[1]
Total gains (losses) on guaranty assets			(6)
Total gains (losses) on partnership investments			(145)
Total gains (losses) on other assets	(209)		(43)
Total gains (losses) on total assets at fair value	(6,490)		(5,927)
Single-Family [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total gains (losses) on acquired property, net	(2,639)		(2,617)
Single-Family [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total gains (losses) on mortgage loans held for investment	(3,077)		(2,244)
Single-Family [Member] | Consolidated Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total gains (losses) on mortgage loans held for investment	(142)		(235)
Multifamily [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total gains (losses) on acquired property, net	(87)		(65)
Multifamily [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total gains (losses) on mortgage loans held for investment	(348)		(481)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages loans held for sale, at lower of cost or fair value	0		0
Other assets	0		0
Guaranty assets			0
Partnership investments			0
Total assets at fair value	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Single-Family [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Single-Family [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Single-Family [Member] | Consolidated Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Multifamily [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Multifamily [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages loans held for sale, at lower of cost or fair value	3		6,776
Other assets	0		0
Guaranty assets			0
Partnership investments			0
Total assets at fair value	3		6,776
Significant Other Observable Inputs (Level 2) [Member] | Single-Family [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	0		0
Significant Other Observable Inputs (Level 2) [Member] | Single-Family [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Significant Other Observable Inputs (Level 2) [Member] | Single-Family [Member] | Consolidated Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Significant Other Observable Inputs (Level 2) [Member] | Multifamily [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	0		0
Significant Other Observable Inputs (Level 2) [Member] | Multifamily [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages loans held for sale, at lower of cost or fair value	197		535
Other assets	1,537		597
Guaranty assets			27
Partnership investments			107
Total assets at fair value	68,979		63,000
Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	19,498		20,248
Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	44,592		38,150
Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Consolidated Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	882		1,294
Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	363		206
Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	1,910		1,836
Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages loans held for sale, at lower of cost or fair value	200	[2]	7,311	[1],[2]
Other assets	1,537	[3]	597	[3]
Guaranty assets			27
Partnership investments			107
Total assets at fair value	68,982		69,776
Estimated Fair Value [Member] | Sold, Transferred or Liquidated as of Period End [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages loans held for sale, at lower of cost or fair value	73		7,100
Mortgage loans held for investment, at amortized cost	8,100		3,400
Acquired property, net	14,500		10,500
Other assets	411		22
Estimated Fair Value [Member] | Single-Family [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	19,498	[4]	20,248	[4]
Estimated Fair Value [Member] | Single-Family [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	44,592	[5]	38,150	[5]
Estimated Fair Value [Member] | Single-Family [Member] | Consolidated Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	882	[5]	1,294	[5]
Estimated Fair Value [Member] | Multifamily [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	363	[4]	206	[4]
Estimated Fair Value [Member] | Multifamily [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	1,910	[5]	1,836	[5]
Consolidation Acounting Guidance Adopted on January 1, 2010 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total gains (losses) on mortgage loans held for sale			(68)
Consolidation Acounting Guidance Adopted on January 1, 2010 [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages loans held for sale, at lower of cost or fair value			$ 7,100

[1] Includes $7.1 billion of estimated fair value and $68 million in losses due to the adoption of the consolidation accounting guidance.

[2] Includes $73 million and $7.1 billion of mortgage loans held for sale that were sold, deconsolidated, retained as a mortgage-related security or redesignated to mortgage loans held for investment as of December 31, 2011 and 2010, respectively.

[3] Includes $411 million and $22 million of other assets that were sold or transferred as of December 31, 2011 and 2010, respectively.

[4] Includes $14.5 billion and $10.5 billion of acquired properties that were sold or transferred as of December 31, 2011 and 2010, respectively.

[5] Includes $8.1 billion and $3.4 billion of mortgage loans held for investment that were liquidated or transferred to foreclosed properties as of December 31, 2011 and 2010, respectively.