Summary of Significant Accounting Policies Related Parties (Details) - USD ($) $ in Millions		3 Months Ended
	Mar. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Jun. 04, 2008
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
Preferred Stock, Shares Issued	555,374,922		555,374,922		555,374,922	1
Payments of cash dividends on senior preferred stock to Treasury	$ 5,500		$ 5,471	$ 2,859
Net worth	3,400		3,400		$ 6,100
Income Taxes Paid			0	360
Unpaid principal balance guaranteed by a related party	$ 5,300		5,300
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees			$ 503	440
Basis Points of Each Dollar of Unpaid Principal Balance	0.042%		0.042%
Trading, at fair value (includes $1,066 and $1,277, respectively, pledged as collateral )	$ 37,684		$ 37,684		40,562
Interest Receivable	7,704		7,704		7,737
Interest income recognized on Treasury securities			142	120
Scenario, Forecast [Member]
Related Parties [Line Items]
Expected undeclared dividends payable on senior preferred stock for the next quarter		$ 2,800
US Treasury [Member]
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement	116,100		116,100		116,100
Initial aggregate liquidation preference of senior preferred stock held by US Treasury	1,000		1,000
Aggregate liquidation preference of senior preferred stock	117,100		117,100
Total available funding from US Treasury pursuant to the senior preferred stock agreement	$ 117,600		$ 117,600
Capital Reserve Amount, current year, Senior Preferred Stock Purchase Agreement, Amendment					600
Percentage of common shares attributable to warrants issued to US Treasury as percentage to total diluted common shares	79.90%		79.90%
Home Affordable Modification Program administrative expense reimbursements from Treasury and Freddie Mac			$ 12	16
Percentage of initial principal loss US Treasury will bear for New Issue Bond Program	35.00%		35.00%
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees			$ 503	440
US Treasury [Member] | Single-family [Member]
Related Parties [Line Items]
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees			503	440
Recognized TCCA fees that had not been remitted to Treasury as of period end	$ 503		503
Freddie Mac [Member] | Freddie Mac [Member]
Related Parties [Line Items]
Interest Receivable	4		4		5
Fair value of mortgage-related securities	1,100		1,100		1,400
Interest income recognized on mortgage-related securities			13	45
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees			30	28
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire or Advance to Equity Method Investments			35	30
U.S. Treasury securities [Member]
Related Parties [Line Items]
Trading, at fair value (includes $1,066 and $1,277, respectively, pledged as collateral )	30,155		30,155		32,317
U.S. Treasury securities [Member] | US Treasury [Member]
Related Parties [Line Items]
Trading, at fair value (includes $1,066 and $1,277, respectively, pledged as collateral )	30,200		30,200		32,300
Interest Receivable	42		42		$ 39
Interest income recognized on Treasury securities			63	32
Other Expense [Member] | US Treasury [Member]
Related Parties [Line Items]
Affordable Housing Program Assessments			29	$ 25
Recognized affordable housing program expenses that had not been remitted to Treasury as of period end	$ 29		$ 29