Mortgage Loans Credit Quality Indicators - MF (Details) (USD $)	Jun. 30, 2012		Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 2,992,247,000,000	[1]	$ 2,978,891,000,000	[1]
Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	183,349,000,000	[1],[2],[3]	179,221,000,000	[1],[2],[3]
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Green [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	142,759,000,000	[1],[3]	131,740,000,000	[1],[3]
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Yellow [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	23,314,000,000	[1],[3],[4]	28,354,000,000	[1],[3],[4]
Unpaid principal balance loans with no available financial information surrounding credit quality	5,600,000,000		6,900,000,000
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Orange [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	16,164,000,000	[1],[3]	17,355,000,000	[1],[3]
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Red [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 1,112,000,000	[1],[3]	$ 1,772,000,000	[1],[3]

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

[2] Multifamily loans 60-89 days delinquent are included in the seriously delinquent column.

[3] Green (loan with acceptable risk); yellow (loan with signs of potential weakness); orange (loan with a well defined weakness that may jeopardize the timely full repayment); and red (loan with a weakness that makes timely collection or liquidation in full more questionable based on existing conditions and values).

[4] Includes approximately $5.6 billion and $6.9 billion of unpaid principal balance as of June 30, 2012 and December 31, 2011, respectively, classified as yellow due to no available financial information.