Mortgage Loans TDRs with Sub Defaults (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) contracts	Dec. 31, 2018 USD ($) contracts	Dec. 31, 2017 USD ($) contracts
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	17,851	21,744	22,980
Recorded investment troubled debt restructurings subsequent default | $	$ 2,758	$ 3,224	$ 3,289
Single-Family [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	17,849	21,742	22,978
Recorded investment troubled debt restructurings subsequent default | $	$ 2,740	$ 3,221	$ 3,277
Single-Family [Member] | Primary [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	15,875	18,613	19,539
Recorded investment troubled debt restructurings subsequent default | $	$ 2,425	$ 2,697	$ 2,722
Single-Family [Member] | Government [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	74	55	91
Recorded investment troubled debt restructurings subsequent default | $	$ 10	$ 7	$ 10
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	1,453	2,412	2,588
Recorded investment troubled debt restructurings subsequent default | $	$ 218	$ 386	$ 400
Single-Family [Member] | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	447	662	760
Recorded investment troubled debt restructurings subsequent default | $	$ 87	$ 131	$ 145
Multifamily [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	2	2	2
Recorded investment troubled debt restructurings subsequent default | $	$ 18	$ 3	$ 12