Fair Value Nonrecurring Changes - Prior to Adoption (Details) (Fair Value, Measurements, Nonrecurring [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Losses on Mortgage loans held for sale	$ (3)	$ (16)
Total Losses on Other assets	(29)	(94)
Total Losses on Total assets at fair value	(1,960)	(4,885)
Single-Family [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Losses on Acquired property, net	(635)	(2,147)
Single-Family [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Losses on Mortgage loans held for investment	(1,045)	(2,125)
Single-Family [Member] | Consolidated Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Losses on Mortgage loans held for investment	(33)	(131)
Multifamily [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Losses on Acquired property, net	(32)	(81)
Multifamily [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Losses on Mortgage loans held for investment	(183)	(291)
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
Other assets		0
Total assets at fair value		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
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
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
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
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
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		2
Other assets		0
Total assets at fair value		2
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
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
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
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
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
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		204
Other assets		1,138
Total assets at fair value		62,172
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		17,642
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		40,280
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		885
Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net		315
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		1,708
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		206	[1]
Other assets		1,138	[2]
Total assets at fair value		62,174
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		72
Mortgage loans held for investment, at amortized cost		5,700
Acquired property, net		11,800
Other assets		285
Estimated Fair Value [Member] | Single-Family [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net		17,642	[3]
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		40,280	[4]
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		885	[4]
Estimated Fair Value [Member] | Multifamily [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net		315	[3]
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		$ 1,708	[4]

[1] Includes $72 million 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 September 30, 2011.

[2] Includes $285 million of other assets that were sold or transferred as of September 30, 2011.

[3] Includes $11.8 billion of acquired properties that were sold or transferred as of September 30, 2011.

[4] Includes $5.7 billion of mortgage loans held for investment that were liquidated or transferred to foreclosed properties as of September 30, 2011.