Summary of Significant Accounting Policies Related Parties (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended			9 Months Ended
	Sep. 29, 2017	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2018	Jun. 30, 2017	Dec. 31, 2016	Sep. 08, 2008	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		1,000,000
Senior Preferred Stock, Par or Stated Value Per Share										$ 1,000
Payments of cash dividends on senior preferred stock to Treasury	$ 3,100				$ 11,367	$ 6,647
Net worth								$ 3,700
Stockholders' Equity Attributable to Parent			$ 3,648		3,648				$ 6,071
Income Taxes Paid			600	$ 531	1,670	1,141
Unpaid principal balance guaranteed by a related party			5,000		5,000
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees			$ 531	465	$ 1,552	1,358
Basis Points of Each Dollar of Unpaid Principal Balance			0.042%		0.042%
Trading, at fair value (includes $727 and $1,277, respectively, pledged as collateral)			$ 36,886		$ 36,886				40,562
Interest Receivable			8,097		8,097				7,737
Interest income recognized on Treasury securities			195	140	513	388
Scenario, Forecast [Member]
Related Parties [Line Items]
Expected undeclared dividends payable on senior preferred stock for the next quarter		$ 3,000
US Treasury [Member]
Related Parties [Line Items]
Total available funding from US Treasury pursuant to the senior preferred stock agreement			117,600		117,600
Capital Reserve Amount, Prior year, Senior Preferred Stock Purchase Agreement, Amendment									1,200
Capital Reserve Amount, current year, Senior Preferred Stock Purchase Agreement, Amendment			600		600
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement			116,100		116,100				116,100
Aggregate liquidation preference of senior preferred stock			$ 117,100		$ 117,100
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			$ 9	14	$ 32	45
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			$ 531	465	$ 1,552	1,358
US Treasury [Member] | Single-family [Member]
Related Parties [Line Items]
Recognized TCCA fees that had not been remitted to Treasury as of period end			531		531
US Treasury [Member] | Scenario, Forecast [Member]
Related Parties [Line Items]
Capital Reserve Amount, Fiscal Year, Senior Preferred Stock Purchase Agreement, Amendment							$ 0
Freddie Mac [Member] | Freddie Mac [Member]
Related Parties [Line Items]
Interest Receivable			3		3				5
Fair value of mortgage-related securities			651		651				1,400
Interest income recognized on mortgage-related securities			8	19	31	100
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees			26	28	82	84
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire or Advance to Equity Method Investments			25	23	78	88
U.S. Treasury securities [Member]
Related Parties [Line Items]
Trading, at fair value (includes $727 and $1,277, respectively, pledged as collateral)			30,799		30,799				32,317
U.S. Treasury securities [Member] | US Treasury [Member]
Related Parties [Line Items]
Trading, at fair value (includes $727 and $1,277, respectively, pledged as collateral)			30,800		30,800				32,300
Interest Receivable			74		74				$ 39
Interest income recognized on Treasury securities			95	40	244	105
Other Expense [Member] | US Treasury [Member]
Related Parties [Line Items]
Affordable Housing Program Assessments			32	$ 40	91	$ 96
Recognized affordable housing program expenses that had not been remitted to Treasury as of period end			$ 91		$ 91