Mortgage Loans TDRs with Sub Defaults (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) contracts	Dec. 31, 2017 USD ($) contracts	Dec. 31, 2016 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	21,744	22,980	25,043
Recorded investment troubled debt restructurings subsequent default | $	$ 3,224	$ 3,289	$ 3,667
Single-Family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	21,742	22,978	25,038
Recorded investment troubled debt restructurings subsequent default | $	$ 3,221	$ 3,277	$ 3,621
Single-Family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	18,613	19,539	20,810
Recorded investment troubled debt restructurings subsequent default | $	$ 2,697	$ 2,722	$ 2,938
Single-Family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	55	91	95
Recorded investment troubled debt restructurings subsequent default | $	$ 7	$ 10	$ 11
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	2,412	2,588	3,131
Recorded investment troubled debt restructurings subsequent default | $	$ 386	$ 400	$ 500
Single-Family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	662	760	1,002
Recorded investment troubled debt restructurings subsequent default | $	$ 131	$ 145	$ 172
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	2	2	5
Recorded investment troubled debt restructurings subsequent default | $	$ 3	$ 12	$ 46