Summary of Significant Accounting Policies Related Parties (Details) - USD ($)	3 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Mar. 31, 2015	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		$ 2,859,000,000	$ 1,920,000,000
Net worth		2,119,000,000		$ 4,059,000,000
Income Taxes Paid		360,000,000	0
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees		$ 440,000,000	382,000,000
Basis Points of Each Dollar of Unpaid Principal Balance		0.042%
Trading, at fair value (includes $1,200 and $135, respectively, pledged as collateral)		$ 40,000,000,000		39,908,000,000
Interest Receivable		7,978,000,000		7,726,000,000
Trading securities		120,000,000	115,000,000
Scenario, Forecast [Member]
Related Parties [Line Items]
Expected undeclared dividends payable on senior preferred stock for the next quarter	$ 919,000,000
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
Initial aggregate liquidation preference of senior preferred stock held by US Treasury		1,000,000,000
Aggregate liquidation preference of senior preferred stock		117,100,000,000
Total available funding from US Treasury pursuant to the senior preferred stock agreement		117,600,000,000
Capital Reserve Amount, current year, Senior Preferred Stock Purchase Agreement, Amendment		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
Percentage of common shares attributable to warrants issued to US Treasury as percentage to total diluted common shares		79.90%
Home Affordable Modification Program administrative expense reimbursements from Treasury and Freddie Mac		$ 16,000,000	16,000,000
Income Taxes Paid		360,000,000	0
Proceeds from Income Tax Refunds		$ 0	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%
Loss of principal or interest under Treasury's Temporary Credit and Liquidity Facility and New Issue Bond Programs		$ 0
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees		440,000,000	382,000,000
Payments for Affordable Housing Programs		111,000,000
US Treasury [Member] | Single-family [Member]
Related Parties [Line Items]
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees		440,000,000	382,000,000
Recognized TCCA fees that had not been remitted to Treasury as of period end		440,000,000
US Treasury [Member] | New Issue Bond Program [Member]
Related Parties [Line Items]
Principal and interest outstanding		3,700,000,000	3,700,000,000
Freddie Mac [Member] | Freddie Mac [Member]
Related Parties [Line Items]
Interest Receivable		18,000,000		22,000,000
Fair value of mortgage-related securities		4,600,000,000		5,600,000,000
Interest income recognized		45,000,000	61,000,000
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees		28,000,000	28,000,000
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire Equity Method Investments		30,000,000	13,000,000
U.S. Treasury securities [Member]
Related Parties [Line Items]
Trading, at fair value (includes $1,200 and $135, respectively, pledged as collateral)		30,746,000,000		29,485,000,000
U.S. Treasury securities [Member] | US Treasury [Member]
Related Parties [Line Items]
Trading, at fair value (includes $1,200 and $135, respectively, pledged as collateral)		30,700,000,000		29,500,000,000
Interest Receivable		23,000,000		$ 15,000,000
Trading securities		32,000,000	4,000,000
Other Expense [Member] | US Treasury [Member]
Related Parties [Line Items]
Affordable Housing Program Assessments		$ 25,000,000	$ 18,000,000