Mortgage Loans Credit Quality Indicators - MF (Details) (USD $)	Mar. 31, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 3,012,435,000,000	[1]	$ 3,007,471,000,000	[1]
Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	190,222,000,000	[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	160,438,000,000	[1],[2]	154,235,000,000	[1],[2]
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Yellow [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	16,435,000,000	[1],[2],[4]	21,304,000,000	[1],[2],[4]
Unpaid principal balance loans with no available financial information surrounding credit quality	4,400,000,000		5,100,000,000
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Orange [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	11,886,000,000	[1],[2]	14,199,000,000	[1],[2]
Multifamily [Member] | Credit Risk Profile by Internally Assigned Grade: Red [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 1,463,000,000	[1],[2]	$ 1,313,000,000	[1],[2]

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

[2] 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).

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

[4] Includes approximately $4.4 billion and $5.1 billion of unpaid principal balance as of March 31, 2013 and December 31, 2012, respectively, classified as yellow due to no available financial information.