Fair Value Nonrecurring Changes in Fair Value (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	$ 0		$ 0
Mortgage loans held for investment, at amortized cost	0		0
Total assets	109,050		93,736
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	272		267
Mortgage loans held for investment, at amortized cost	2,583,989		2,567,022
Total assets	2,739,230		2,694,632
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	196		208
Mortgage loans held for investment, at amortized cost	449,318		466,594
Total assets	478,138		495,561
Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	468		475
Mortgage loans held for investment, at amortized cost	3,033,307		3,033,616
Total assets	3,312,084		3,268,138
Fair Value, Measurements, Nonrecurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	0		0
Other assets	0		0
Total assets	0		0
Fair Value, Measurements, Nonrecurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	83		104
Other assets	0		0
Total assets	83		104
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	124		135
Other assets	135		384
Total assets	27,224		29,450
Fair Value, Measurements, Nonrecurring [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	207		239
Other assets	135		384
Total assets	27,307		29,554
Fannie Mae [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Fannie Mae [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	35,735		39,018
Fannie Mae [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	223,862		232,170
Fannie Mae [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	259,597		271,188
Consolidated Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	12,602		10,800
Consolidated Trusts [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Consolidated Trusts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	2,548,254		2,528,004
Consolidated Trusts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	225,456		234,424
Consolidated Trusts [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	2,773,710		2,762,428
Single-Family [Member] | Fair Value, Measurements, Nonrecurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	0		0
Single-Family [Member] | Fair Value, Measurements, Nonrecurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	0		0
Single-Family [Member] | Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	2,915		3,692
Single-Family [Member] | Fair Value, Measurements, Nonrecurring [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquired property, net	2,915		3,692
Single-Family [Member] | Fannie Mae [Member] | Fair Value, Measurements, Nonrecurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0	[1]	0	[1]
Single-Family [Member] | Fannie Mae [Member] | Fair Value, Measurements, Nonrecurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0	[1]	0	[1]
Single-Family [Member] | Fannie Mae [Member] | Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	22,020	[1]	23,314	[1]
Single-Family [Member] | Fannie Mae [Member] | Fair Value, Measurements, Nonrecurring [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	22,020	[1]	23,314	[1]
Single-Family [Member] | Consolidated Trusts [Member] | Fair Value, Measurements, Nonrecurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0	[1]	0	[1]
Single-Family [Member] | Consolidated Trusts [Member] | Fair Value, Measurements, Nonrecurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0	[1]	0	[1]
Single-Family [Member] | Consolidated Trusts [Member] | Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	161	[1]	227	[1]
Single-Family [Member] | Consolidated Trusts [Member] | Fair Value, Measurements, Nonrecurring [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	161	[1]	227	[1]
Multifamily [Member] | Fair Value, Measurements, Nonrecurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Acquired property, net	0		0
Multifamily [Member] | Fair Value, Measurements, Nonrecurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	0		0
Acquired property, net	0		0
Multifamily [Member] | Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	1,846		1,624
Acquired property, net	23		74
Multifamily [Member] | Fair Value, Measurements, Nonrecurring [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for investment, at amortized cost	1,846		1,624
Acquired property, net	$ 23		$ 74

[1] Excludes estimated recoveries from mortgage insurance proceeds.