Mortgage Loans Credit Quality Indicators - SF (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 2,992,247	[1]	$ 2,978,891	[1]
Single-Family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,808,898	[1]	2,799,670	[1]
Single-Family [Member] | Primary [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,512,247	[1],[2],[3],[4]	2,481,156	[1],[2],[3],[4]
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	1,582,116	[1],[2],[3],[4]	1,464,348	[1],[2],[3],[4]
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	372,620	[1],[2],[3],[4]	412,342	[1],[2],[3],[4]
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	233,739	[1],[2],[3],[4]	246,648	[1],[2],[3],[4]
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	116,616	[1],[2],[3],[4]	128,428	[1],[2],[3],[4]
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	67,940	[1],[2],[3],[4]	73,836	[1],[2],[3],[4]
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	24,343	[1],[2],[3],[4]	25,750	[1],[2],[3],[4]
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	114,873	[1],[2],[3],[4]	129,804	[1],[2],[3],[4]
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	164,972	[1],[2],[3]	177,412	[1],[2],[3]
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	58,906	[1],[2],[3]	61,618	[1],[2],[3]
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	19,484	[1],[2],[3]	21,369	[1],[2],[3]
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	18,011	[1],[2],[3]	19,790	[1],[2],[3]
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	15,292	[1],[2],[3]	16,164	[1],[2],[3]
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	11,992	[1],[2],[3]	12,534	[1],[2],[3]
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	4,852	[1],[2],[3]	5,087	[1],[2],[3]
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	36,435	[1],[2],[3]	40,850	[1],[2],[3]
Single-Family [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	80,339	[1],[2],[3],[5]	89,226	[1],[2],[3],[5]
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	22,573	[1],[2],[3],[5]	23,414	[1],[2],[3],[5]
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	8,067	[1],[2],[3],[5]	9,224	[1],[2],[3],[5]
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	8,228	[1],[2],[3],[5]	9,445	[1],[2],[3],[5]
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	7,985	[1],[2],[3],[5]	8,951	[1],[2],[3],[5]
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	7,223	[1],[2],[3],[5]	7,912	[1],[2],[3],[5]
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	3,118	[1],[2],[3],[5]	3,557	[1],[2],[3],[5]
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	23,145	[1],[2],[3],[5]	26,723	[1],[2],[3],[5]
Single-Family [Member] | Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 51,340	[1],[6]	$ 51,876	[1],[6]

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

[2] Excludes $51.3 billion and $51.9 billion as of June 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.

[3] 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.

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

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

[6] 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.