Summary of Significant Accounting Policies Related Parties (Details) - USD ($)			1 Months Ended	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Jul. 31, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015	Dec. 31, 2014
Related Parties [Line Items]
Number of days after which we have not been paying debts or liabilities exceed assets FHFA must place us into receivership						60 days
Payments of cash dividends on senior preferred stock to Treasury		$ 1,800,000,000				$ 3,716,000,000	$ 12,882,000,000
Net worth		$ 6,159,000,000		$ 6,159,000,000		6,159,000,000		$ 3,600,000,000	$ 3,720,000,000
Income Taxes Paid						370,000,000	2,475,000,000
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees				397,000,000	$ 335,000,000	779,000,000	657,000,000
Other expense				$ 205,000,000	276,000,000	$ 208,000,000	407,000,000
Basis points of each dollar of unpaid principal balance		420.00%		420.00%		420.00%
Scenario, Forecast [Member]
Related Parties [Line Items]
Expected undeclared dividends payable on senior preferred stock for the next quarter	$ 4,400,000,000
US Treasury [Member]
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement		$ 116,100,000,000		$ 116,100,000,000		$ 116,100,000,000
Initial aggregate liquidation preference of senior preferred stock held by US Treasury		1,000,000,000		1,000,000,000		1,000,000,000
Aggregate liquidation preference of senior preferred stock		117,100,000,000		117,100,000,000		117,100,000,000
Total available funding from US Treasury pursuant to the senior preferred stock agreement		117,600,000,000		117,600,000,000		117,600,000,000
Capital Reserve Amount, current year, Senior Preferred Stock Purchase Agreement, Amendment		1,800,000,000		1,800,000,000		1,800,000,000
Capital Reserve Amount, prior year, Senior Preferred Stock Purchase Agreement, Amendment									2,400,000,000
Annual Reduction of Capital Reserve Amount from 2013 to 2018, Senior Preferred Stock Purchase Agreement, Amendment		$ 600,000,000		$ 600,000,000		$ 600,000,000
Percentage of common shares attributable to warrants issued to US Treasury as percentage to total diluted common shares		79.90%		79.90%		79.90%
Home Affordable Modification Program administrative expense reimbursements from Treasury and Freddie Mac				$ 16,000,000	20,000,000	$ 32,000,000	37,000,000
Income Taxes Paid				$ 370,000,000	2,100,000,000	370,000,000	2,500,000,000
Proceeds from Income Tax Refunds						$ 135,000,000
Percentage of initial principal loss US Treasury will bear for Temporary Credit and Liquidity Facilities and New Issue Bond Programs		35.00%		35.00%		35.00%
Loss of principal or interest under Treasury's Temporary Credit and Liquidity Facility and New Issue Bond Programs		$ 0		$ 0		$ 0
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees				397,000,000	335,000,000	779,000,000	657,000,000
US Treasury [Member] | Affordable Housing Allocation [Member]
Related Parties [Line Items]
Other expense				60,000,000		112,000,000
US Treasury [Member] | Single-family [Member]
Related Parties [Line Items]
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees				397,000,000	335,000,000	779,000,000	657,000,000
Recognized TCCA fees that had not been remitted to Treasury as of period end		397,000,000		397,000,000		397,000,000
US Treasury [Member] | Temporary Credit and Liquidity Facilities Program [Member]
Related Parties [Line Items]
Principal and interest outstanding		272,000,000		272,000,000		272,000,000			390,000,000
US Treasury [Member] | New Issue Bond Program [Member]
Related Parties [Line Items]
Principal and interest outstanding		3,900,000,000		3,900,000,000		3,900,000,000			4,200,000,000
US Treasury [Member] | Subsequent Event [Member]
Related Parties [Line Items]
Proceeds from Income Tax Refunds			$ 142,000,000
Freddie Mac [Member] | Freddie Mac [Member]
Related Parties [Line Items]
Fair value of mortgage-related securities		$ 6,500,000,000		6,500,000,000		6,500,000,000			$ 6,900,000,000
Interest income recognized				58,000,000	73,000,000	119,000,000	151,000,000
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees				28,000,000	26,000,000	56,000,000	54,000,000
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire Equity Method Investments				$ 17,000,000	$ 0	$ 30,000,000	$ 0