Mortgage Loans Credit Quality Indicators - MF (Details) (USD $)	Jun. 30, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 3,021,416,000,000	[1]	$ 3,007,471,000,000	[1]
Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	190,536,000,000	[1],[2],[3]	191,051,000,000	[1],[2],[3]
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Green [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	161,420,000,000	[1],[3]	154,235,000,000	[1],[3]
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Yellow [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	16,644,000,000	[1],[3],[4]	21,304,000,000	[1],[3],[4]
Unpaid principal balance of loans with no available current financial information	3,400,000,000		5,100,000,000
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Orange [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	11,260,000,000	[1],[3]	14,199,000,000	[1],[3]
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Red [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 1,212,000,000	[1],[3]	$ 1,313,000,000	[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 $3.4 billion and $5.1 billion of unpaid principal balance as of June 30, 2013 and December 31, 2012, respectively, classified as yellow due to no available current financial information.