Summary of Significant Accounting Policies Related Parties (Details) - USD ($)		3 Months Ended		9 Months Ended
	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2020	Dec. 31, 2018
Related Parties [Line Items]
Deficit Of Core Capital Over Statutory Minimum Capital Requirement		$ (133,800,000,000)		$ (133,800,000,000)			$ (137,100,000,000)
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement		119,800,000,000		119,800,000,000
Net worth	$ 6,400,000,000	10,342,000,000		10,342,000,000			6,240,000,000
Payments of cash dividends on senior preferred stock to Treasury		0	$ 4,459,000,000	5,601,000,000	$ 5,397,000,000
Income Taxes Paid		0		$ 1,250,000,000	$ 460,000,000
Weighted Average Number of Shares, Contingently Issuable				4,600,000,000	4,600,000,000
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees		$ 613,000,000	576,000,000	$ 1,806,000,000	$ 1,698,000,000
Basis Points of Each Dollar of Unpaid Principal Balance		0.042%		0.042%
Trading, at fair value (includes $4,304 and $3,061, respectively, pledged as collateral)		$ 44,206,000,000		$ 44,206,000,000			41,867,000,000
Interest Receivable		8,923,000,000		8,923,000,000			8,490,000,000
Interest income recognized on Treasury securities		418,000,000	363,000,000	$ 1,277,000,000	$ 917,000,000
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Preferred Stock				131,000,000	131,000,000
Affordable Housing Program Obligation		0.35		$ 0.35
Forecast [Member]
Related Parties [Line Items]
Cumulative Effect Of New Accounting Principle In Period Of Adoption						$ 2,000,000,000
US Treasury [Member]
Related Parties [Line Items]
Total available funding from US Treasury pursuant to the senior preferred stock agreement		113,900,000,000		113,900,000,000
Capital Reserve Amount, Fiscal Year, Senior Preferred Stock Purchase Agreement, Amendment	3,000,000,000
Capital Reserve Amount, current year, Senior Preferred Stock Purchase Agreement, Amendment		25,000,000,000		25,000,000,000
Aggregate liquidation preference of senior preferred stock	123,800,000,000	127,200,000,000		127,200,000,000			$ 131,200,000,000
Increase in Aggregate Liquidation Preference of Senior Preferred Stock	3,400,000,000	$ 4,000,000,000.0		$ 4,000,000,000.0
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		$ 5,000,000	6,000,000	$ 15,000,000	$ 19,000,000
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees		613,000,000	576,000,000	1,806,000,000	1,698,000,000
Affordable Housing Program Obligation		75,000,000		75,000,000
US Treasury [Member] | Single-family [Member]
Related Parties [Line Items]
Recognized TCCA fees that had not been remitted to Treasury as of period end		613,000,000		613,000,000
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees		30,000,000	26,000,000	89,000,000	81,000,000
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire or Advance to Equity Method Investments		22,000,000	33,000,000	84,000,000	109,000,000
Other Expense [Member] | US Treasury [Member]
Related Parties [Line Items]
Affordable Housing Program Assessments	$ 75,000,000	$ 32,000,000	$ 20,000,000	$ 68,000,000	$ 57,000,000