Summary of Significant Accounting Policies Related Parties (Details) - USD ($)		3 Months Ended			9 Months Ended
	Sep. 30, 2015	Dec. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 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	$ 4,400,000,000				$ 8,075,000,000	$ 16,594,000,000
Net worth	$ 4,003,000,000		$ 4,003,000,000		4,003,000,000		$ 6,200,000,000	$ 3,720,000,000
Income Taxes Paid					470,000,000	2,475,000,000
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees			413,000,000	$ 351,000,000	1,192,000,000	1,008,000,000
Other expense			$ 204,000,000	72,000,000	$ 412,000,000	479,000,000
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		$ 2,200,000,000
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		$ 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			$ 18,000,000	18,000,000	$ 50,000,000	55,000,000
Income Taxes Paid			$ 100,000,000		470,000,000	2,500,000,000
Proceeds from Income Tax Refunds					$ 277,000,000
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			413,000,000	351,000,000	1,192,000,000	1,008,000,000
US Treasury [Member] | Affordable Housing Allocation [Member]
Related Parties [Line Items]
Other expense			56,000,000		168,000,000
US Treasury [Member] | Single-family [Member]
Related Parties [Line Items]
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees			413,000,000	351,000,000	1,192,000,000	1,008,000,000
Recognized TCCA fees that had not been remitted to Treasury as of period end	413,000,000		413,000,000		413,000,000
US Treasury [Member] | Temporary Credit and Liquidity Facilities Program [Member]
Related Parties [Line Items]
Principal and interest outstanding	0		0		0			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
Freddie Mac [Member] | Freddie Mac [Member]
Related Parties [Line Items]
Fair value of mortgage-related securities	$ 6,100,000,000		6,100,000,000		6,100,000,000			$ 6,900,000,000
Interest income recognized			55,000,000	68,000,000	174,000,000	219,000,000
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees			28,000,000	26,000,000	84,000,000	80,000,000
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire Equity Method Investments			$ 17,000,000	$ 0	$ 47,000,000	$ 0