Summary of Significant Accounting Policies Related Parties (Details) - USD ($)		3 Months Ended			9 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Dec. 31, 2015
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	$ 2,900,000,000				$ 6,647,000,000	$ 8,075,000,000
Net worth	4,176,000,000		$ 4,176,000,000		4,176,000,000		$ 4,100,000,000	$ 4,059,000,000
Income Taxes Paid					1,141,000,000	470,000,000
Unpaid principal balance guaranteed by a related party	$ 6,500,000,000		6,500,000,000		6,500,000,000
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees			$ 465,000,000	$ 413,000,000	$ 1,358,000,000	1,192,000,000
Basis Points of Each Dollar of Unpaid Principal Balance	0.042%		0.042%		0.042%
Trading, at fair value (includes $1,191 and $135, respectively, pledged as collateral)	$ 40,547,000,000		$ 40,547,000,000		$ 40,547,000,000			39,908,000,000
Interest Receivable	7,728,000,000		7,728,000,000		7,728,000,000			7,726,000,000
Interest income recognized on Treasury securities			140,000,000	99,000,000	388,000,000	330,000,000
Scenario, Forecast [Member]
Related Parties [Line Items]
Expected undeclared dividends payable on senior preferred stock for the next quarter		$ 3,000,000,000
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	1,200,000,000		1,200,000,000		1,200,000,000		$ 1,200,000,000
Capital Reserve Amount, prior year, Senior Preferred Stock Purchase Agreement, Amendment								1,800,000,000
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			$ 14,000,000	18,000,000	$ 45,000,000	50,000,000
Income Taxes Paid			$ 531,000,000	100,000,000	1,141,000,000	470,000,000
Proceeds from Income Tax Refunds					$ 0	277,000,000
Percentage of initial principal loss US Treasury will bear for New Issue Bond Program	35.00%		35.00%		35.00%
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees			$ 465,000,000	413,000,000	$ 1,358,000,000	1,192,000,000
US Treasury [Member] | Single-family [Member]
Related Parties [Line Items]
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees			465,000,000	413,000,000	1,400,000,000	1,200,000,000
Recognized TCCA fees that had not been remitted to Treasury as of period end	$ 465,000,000		465,000,000		465,000,000
Freddie Mac [Member] | Freddie Mac [Member]
Related Parties [Line Items]
Interest Receivable	5,000,000		5,000,000		5,000,000			22,000,000
Fair value of mortgage-related securities	1,400,000,000		1,400,000,000		1,400,000,000			5,600,000,000
Interest income recognized on mortgage-related securities			19,000,000	55,000,000	100,000,000	174,000,000
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees			28,000,000	28,000,000	84,000,000	84,000,000
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire or Advance to Equity Method Investments			23,000,000	17,000,000	88,000,000	47,000,000
U.S. Treasury securities [Member]
Related Parties [Line Items]
Trading, at fair value (includes $1,191 and $135, respectively, pledged as collateral)	31,277,000,000		31,277,000,000		31,277,000,000			29,485,000,000
U.S. Treasury securities [Member] | US Treasury [Member]
Related Parties [Line Items]
Trading, at fair value (includes $1,191 and $135, respectively, pledged as collateral)	31,300,000,000		31,300,000,000		31,300,000,000			29,500,000,000
Interest Receivable	28,000,000		28,000,000		28,000,000			$ 15,000,000
Interest income recognized on Treasury securities			40,000,000	8,000,000	105,000,000	17,000,000
Other Expense [Member] | US Treasury [Member]
Related Parties [Line Items]
Affordable Housing Program Assessments			40,000,000	$ 56,000,000	96,000,000	$ 168,000,000
Recognized affordable housing program expenses that had not been remitted to Treasury as of period end	$ 96,000,000		$ 96,000,000		$ 96,000,000