Summary of Significant Accounting Policies Related Parties (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Related Parties [Line Items]
Deficit Of Core Capital Over Statutory Minimum Capital Requirement	$ (128,100,000,000)		$ (128,100,000,000)					$ (128,800,000,000)
Net worth	20,693,000,000		20,693,000,000			$ 16,500,000,000		14,608,000,000
Aggregate liquidation preference of senior preferred stock	138,000,000,000.0		138,000,000,000.0
Payments of cash dividends on senior preferred stock to Treasury	0	$ 0	0	$ 5,601,000,000
Income Taxes Paid			2,750,000,000	1,250,000,000
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees	$ 679,000,000	613,000,000	$ 1,976,000,000	1,806,000,000
Basis Points of Each Dollar of Unpaid Principal Balance	420.00%		420.00%
Debt Securities, Trading	$ 142,472,000,000		$ 142,472,000,000					48,123,000,000
Interest Receivable	9,748,000,000		9,748,000,000					8,604,000,000
Interest income recognized on Treasury securities	177,000,000	418,000,000	712,000,000	1,277,000,000
Affordable Housing Program Obligation	0.35		0.35
Loans held for sale, at lower of cost or fair value	8,312,000,000		8,312,000,000				$ 6,823,000,000	6,773,000,000
Accumulated deficit	(112,680,000,000)		(112,680,000,000)				(119,915,000,000)	(118,776,000,000)
Allowance for Loan and Lease Losses, Real Estate	11,703,000,000		11,703,000,000				10,738,000,000	9,016,000,000
Other assets	14,959,000,000		14,959,000,000				14,542,000,000	14,312,000,000
Deferred Tax Assets, Net							12,213,000,000	$ 11,910,000,000
Accounting Standards Update 2016-13 [Member]
Related Parties [Line Items]
Loans held for sale, at lower of cost or fair value							50,000,000
Accumulated deficit							(1,139,000,000)
Allowance for Loan and Lease Losses, Real Estate							1,722,000,000
Other assets							230,000,000
Deferred Tax Assets, Net							$ 303,000,000
US Treasury [Member]
Related Parties [Line Items]
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						$ 135,400,000,000
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	5,000,000	$ 14,000,000	15,000,000
Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees	679,000,000	613,000,000	1,976,000,000	1,806,000,000
Total available funding from US Treasury pursuant to the senior preferred stock agreement	113,900,000,000		113,900,000,000
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement	119,800,000,000		119,800,000,000
US Treasury [Member] | Forecast [Member]
Related Parties [Line Items]
Aggregate liquidation preference of senior preferred stock					$ 142,200,000,000
US Treasury [Member] | Single-family [Member]
Related Parties [Line Items]
Recognized TCCA fees that had not been remitted to Treasury as of period end	679,000,000		679,000,000
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees	35,000,000	30,000,000	102,000,000	89,000,000
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire or Advance to Equity Method Investments	19,000,000	22,000,000	67,000,000	84,000,000
Other Expense [Member] | US Treasury [Member]
Related Parties [Line Items]
Affordable Housing Program Assessments	$ 59,000,000	$ 32,000,000	$ 144,000,000	$ 68,000,000