Mortgage Loans TDR (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012 contracts		Sep. 30, 2011 contracts		Sep. 30, 2012 contracts		Sep. 30, 2011 contracts		Dec. 31, 2011
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity	205,467	[1]	79,300		279,251	[1]	173,367
Recorded investment troubled debt restructurings activity	$ 29,249	[1],[2]	$ 14,672	[2]	$ 42,575	[1],[2]	$ 33,136	[2]
Number of loans troubled debt restructurings subsequent default	13,617		19,063		42,709		69,801
Recorded investment troubled debt restructurings subsequent default	2,388	[3]	3,546	[3]	7,701	[3]	13,158	[3]
Single-Family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity	205,463	[1]	79,287		279,226	[1]	173,325
Recorded investment troubled debt restructurings activity	29,230	[1],[2]	14,633	[2]	42,423	[1],[2]	32,922	[2]
Number of loans troubled debt restructurings subsequent default	13,616		19,063		42,706		69,793
Recorded investment troubled debt restructurings subsequent default	2,379	[3]	3,546	[3]	7,689	[3]	13,109	[3]
Troubled debt restructuring recorded investment	190,100				190,100				161,900
Single-Family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity	165,395	[1],[4]	60,725	[4]	224,165	[1],[4]	132,682	[4]
Recorded investment troubled debt restructurings activity	22,068	[1],[2],[4]	10,594	[2],[4]	32,022	[1],[2],[4]	23,783	[2],[4]
Number of loans troubled debt restructurings subsequent default	10,870	[4]	14,545	[4]	33,446	[4]	52,532	[4]
Recorded investment troubled debt restructurings subsequent default	1,798	[3],[4]	2,531	[3],[4]	5,699	[3],[4]	9,227	[3],[4]
Single-Family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity	112	[1],[5]	201	[5]	314	[1],[5]	497	[5]
Recorded investment troubled debt restructurings activity	13	[1],[2],[5]	24	[2],[5]	41	[1],[2],[5]	86	[2],[5]
Number of loans troubled debt restructurings subsequent default	51	[5]	70	[5]	150	[5]	252	[5]
Recorded investment troubled debt restructurings subsequent default	8	[3],[5]	17	[3],[5]	25	[3],[5]	68	[3],[5]
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity	31,088	[1]	12,932		42,026	[1]	27,722
Recorded investment troubled debt restructurings activity	5,284	[1],[2]	2,691	[2]	7,537	[1],[2]	5,958	[2]
Number of loans troubled debt restructurings subsequent default	1,854		2,929		6,113		11,625
Recorded investment troubled debt restructurings subsequent default	377	[3]	620	[3]	1,246	[3]	2,499	[3]
Single-Family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity	8,868	[1],[6]	5,429	[6]	12,721	[1],[6]	12,424	[6]
Recorded investment troubled debt restructurings activity	1,865	[1],[2],[6]	1,324	[2],[6]	2,823	[1],[2],[6]	3,095	[2],[6]
Number of loans troubled debt restructurings subsequent default	841	[6]	1,519	[6]	2,997	[6]	5,384	[6]
Recorded investment troubled debt restructurings subsequent default	196	[3],[6]	378	[3],[6]	719	[3],[6]	1,315	[3],[6]
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity	4	[1]	13		25	[1]	42
Recorded investment troubled debt restructurings activity	19	[1],[2]	39	[2]	152	[1],[2]	214	[2]
Number of loans troubled debt restructurings subsequent default	1		0		3		8
Recorded investment troubled debt restructurings subsequent default	9	[3]	0	[3]	12	[3]	49	[3]
Troubled debt restructuring recorded investment	1,000				1,000				956
Loans Discharged with Bankruptcy Relief [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring, number of loans	170,000				170,000
Troubled debt restructuring recorded investment	$ 22,900				$ 22,900

[1] As of September 30, 2012, we classified as TDRs approximately 170,000 loans to certain borrowers who have received bankruptcy relief. These loans had a recorded investment of $22.9 billion

[2] Recorded investment consists of unpaid principal balance, unamortized premiums, discounts and other cost basis adjustments, and accrued interest receivable. Based on the nature of our modification programs, which do not include principal or interest forgiveness, there is not a material difference between the recorded investment in our loans pre- and post- modification, therefore amounts represent recorded investment post-modification.

[3] Recorded investment consists of unpaid principal balance, unamortized premiums, discounts and other cost basis adjustments, and accrued interest receivable. Represents our recorded investment in the loan at time of payment default.

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

[5] 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.

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