Mortgage Loans - TDRs (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) contract	Jun. 30, 2020 USD ($) contract	Jun. 30, 2021 USD ($) contract	Jun. 30, 2020 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Average term extension of a single-family modified loan	145 months	168 months	142 months	168 months
Average interest rate reduction of a single-family modified loan	0.61%	0.34%	0.57%	0.33%
Number of loans troubled debt restructurings activity | contract	3,426	10,005	6,979	22,615
Recorded investment troubled debt restructurings activity | $	$ 507	$ 1,657	$ 1,030	$ 3,756
Number of loans troubled debt restructurings subsequent default | contract	1,882	5,988	4,677	9,549
Recorded investment troubled debt restructurings subsequent default | $	$ 309	$ 1,178	$ 783	$ 1,756
Single-family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contract	3,426	10,005	6,979	22,615
Recorded investment troubled debt restructurings activity | $	$ 507	$ 1,657	$ 1,030	$ 3,756
Number of loans troubled debt restructurings subsequent default | contract	1,882	5,986	4,677	9,545
Recorded investment troubled debt restructurings subsequent default | $	$ 309	$ 1,164	$ 783	$ 1,740
Multifamily
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contract	0	0	0	0
Recorded investment troubled debt restructurings activity | $	$ 0	$ 0	$ 0	$ 0
Number of loans troubled debt restructurings subsequent default | contract	0	2	0	4
Recorded investment troubled debt restructurings subsequent default | $	$ 0	$ 14	$ 0	$ 16
20- and 30-year or more, amortizing fixed-rate | Single-family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contract	2,907	8,511	5,896	19,367
Recorded investment troubled debt restructurings activity | $	$ 458	$ 1,497	$ 929	$ 3,406
Number of loans troubled debt restructurings subsequent default | contract	1,562	5,398	3,972	8,573
Recorded investment troubled debt restructurings subsequent default | $	$ 262	$ 1,066	$ 675	$ 1,587
15-year or less, amortizing fixed-rate | Single-family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contract	308	796	677	1,869
Recorded investment troubled debt restructurings activity | $	$ 26	$ 68	$ 54	$ 166
Number of loans troubled debt restructurings subsequent default | contract	103	35	197	85
Recorded investment troubled debt restructurings subsequent default | $	$ 8	$ 3	$ 14	$ 6
Adjustable-rate | Single-family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contract	37	142	78	286
Recorded investment troubled debt restructurings activity | $	$ 6	$ 22	$ 12	$ 46
Number of loans troubled debt restructurings subsequent default | contract	6	5	15	12
Recorded investment troubled debt restructurings subsequent default | $	$ 1	$ 1	$ 3	$ 2
Other | Single-family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contract	174	556	328	1,093
Recorded investment troubled debt restructurings activity | $	$ 17	$ 70	$ 35	$ 138
Number of loans troubled debt restructurings subsequent default | contract	211	548	493	875
Recorded investment troubled debt restructurings subsequent default | $	$ 38	$ 94	$ 91	$ 145