Mortgage Loans Credit Quality Indicators - SF (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 3,008,974	[1],[2]	$ 2,978,891	[1]
Single-Family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,822,105	[1],[2]	2,799,670	[1]
Single-Family [Member] | Primary [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,537,778	[1],[3],[4],[5]	2,481,156	[1],[3],[4],[5]
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Less Than or Equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	1,678,404	[1],[3],[4],[5]	1,464,348	[1],[3],[4],[5]
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 80% and Less Than or Equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	350,088	[1],[3],[4],[5]	412,342	[1],[3],[4],[5]
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 90% and Less Than or Equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	219,307	[1],[3],[4],[5]	246,648	[1],[3],[4],[5]
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 100% and Less Than or Equal to 110% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	104,161	[1],[3],[4],[5]	128,428	[1],[3],[4],[5]
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 110% and Less Than or Equal to 120% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	61,721	[1],[3],[4],[5]	73,836	[1],[3],[4],[5]
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 120% and Less Than or Equal to 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	21,803	[1],[3],[4],[5]	25,750	[1],[3],[4],[5]
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	102,294	[1],[3],[4],[5]	129,804	[1],[3],[4],[5]
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	158,280	[1],[3],[4]	177,412	[1],[3],[4]
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Less Than or Equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	59,408	[1],[3],[4]	61,618	[1],[3],[4]
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 80% and Less Than or Equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	19,010	[1],[3],[4]	21,369	[1],[3],[4]
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 90% and Less Than or Equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	17,503	[1],[3],[4]	19,790	[1],[3],[4]
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 100% and Less Than or Equal to 110% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	14,588	[1],[3],[4]	16,164	[1],[3],[4]
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 110% and Less Than or Equal to 120% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	11,261	[1],[3],[4]	12,534	[1],[3],[4]
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 120% and Less Than or Equal to 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	4,504	[1],[3],[4]	5,087	[1],[3],[4]
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	32,006	[1],[3],[4]	40,850	[1],[3],[4]
Single-Family [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	74,968	[1],[3],[4],[6]	89,226	[1],[3],[4],[6]
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Less Than or Equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	22,737	[1],[3],[4],[6]	23,414	[1],[3],[4],[6]
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 80% and Less Than or Equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	7,729	[1],[3],[4],[6]	9,224	[1],[3],[4],[6]
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 90% and Less Than or Equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	7,888	[1],[3],[4],[6]	9,445	[1],[3],[4],[6]
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 100% and Less Than or Equal to 110% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	7,591	[1],[3],[4],[6]	8,951	[1],[3],[4],[6]
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 110% and Less Than or Equal to 120% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	6,709	[1],[3],[4],[6]	7,912	[1],[3],[4],[6]
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 120% and Less Than or Equal to 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,844	[1],[3],[4],[6]	3,557	[1],[3],[4],[6]
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	19,470	[1],[3],[4],[6]	26,723	[1],[3],[4],[6]
Single-Family [Member] | Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 51,079	[1],[7]	$ 51,876	[1],[7]

[1] Recorded investment consists of unpaid principal balance, unamortized premiums, discounts and other cost basis adjustments, and accrued interest receivable.

[2] As of September 30, 2012, we began classifying as TDRs loans to certain borrowers who have received bankruptcy relief. These loans had a recorded investment of $22.9 billion and a related allowance of $1.1 billion as of September 30, 2012.

[3] Excludes $51.1 billion and $51.9 billion as of September 30, 2012 and December 31, 2011, respectively, of mortgage loans guaranteed or insured, in whole or in part, by the U.S. government or one of its agencies that are not Alt-A loans. The segment class is primarily reverse mortgages for which we do not calculate an estimated mark-to-market LTV.

[4] The aggregate estimated mark-to-market LTV ratio is based on the unpaid principal balance of the loan as of the end of each reported period divided by the estimated current value of the property, which we calculate using an internal valuation model that estimates periodic changes in home value.

[5] Consists of mortgage loans that are not included in other loan classes.

[6] Includes loans with higher-risk loan characteristics, such as interest-only loans and negative-amortizing loans that are neither government nor Alt-A.

[7] Consists of mortgage loans guaranteed or insured, in whole or in part, by the U.S. government or one of its agencies that are not Alt-A. Primarily consists of reverse mortgages which due to their nature are not aged and are included in the current column.