Fair Value Level 3 Valuation - Nonrecurring (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	$ 267		$ 208
Mortgage loans held for investment, at amortized cost	406,415		466,594
Total assets at fair value	435,326		495,561
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	132		135
Other assets	110		384
Total assets at fair value	25,502		29,450
Fannie Mae [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	225,059		232,170
Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	13,770		10,800
Consolidated Trusts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	181,356		234,424
Single-Family [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	2,893		3,692
Single-Family [Member] | Fannie Mae [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	20,316	[1]	23,314	[1]
Single-Family [Member] | Consolidated Trusts [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	123	[1]	227	[1]
Multifamily [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	1,887		1,624
Acquired property, net	41		74
Proprietary home price model and appraisals [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Number of properties measured	76.00%		78.00%
Consensus without Inputs [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	132		135
Internal Model [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Other assets	61		203
Internal Model [Member] | Single-Family [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	610		1,014
Internal Model [Member] | Single-Family [Member] | Fannie Mae [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	20,316		23,314
Internal Model [Member] | Single-Family [Member] | Consolidated Trusts [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	123		227
Appraisals [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Other assets	25		8
Appraisals [Member] | Single-Family [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	1,078		467
Appraisals [Member] | Multifamily [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	127		194
Acquired property, net	2		8
Walk Forwards [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Other assets	10		43
Walk Forwards [Member] | Single-Family [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	546		1,348
Broker Price Opinions [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Other assets	10		0
Broker Price Opinions [Member] | Multifamily [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	420		395
Acquired property, net	34		46
Asset Manager Estimate [Member] | Multifamily [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	1,056		1,001
Other Valuation Technique [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Other assets	4		130
Other Valuation Technique [Member] | Single-Family [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	39		76
Other Valuation Technique [Member] | Multifamily [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at amortized cost	284		34
Accepted Offers [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Number of properties measured	21.00%		20.00%
Accepted Offers [Member] | Single-Family [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	620		787
Accepted Offers [Member] | Multifamily [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	$ 5		$ 20

[1] Excludes estimated recoveries from mortgage insurance proceeds.