Mortgage Loans - TDRs (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021 USD ($) contract	Jun. 30, 2021 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Average term extension of a single-family modified loan	145 months	142 months
Average interest rate reduction of a single-family modified loan	0.61%	0.57%
Number of loans, troubled debt restructurings activity | contract	3,426	6,979
Amortized cost, troubled debt restructurings activity | $	$ 507	$ 1,030
Number of loans, troubled debt restructurings subsequent default | contract	1,882	4,677
Amortized cost, troubled debt restructurings subsequent default | $	$ 309	$ 783
Single-family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans, troubled debt restructurings activity | contract	3,426	6,979
Amortized cost, troubled debt restructurings activity | $	$ 507	$ 1,030
Number of loans, troubled debt restructurings subsequent default | contract	1,882	4,677
Amortized cost, troubled debt restructurings subsequent default | $	$ 309	$ 783
Multifamily
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans, troubled debt restructurings activity | contract	0	0
Amortized cost, troubled debt restructurings activity | $	$ 0	$ 0
Number of loans, troubled debt restructurings subsequent default | contract	0	0
Amortized cost, troubled debt restructurings subsequent default | $	$ 0	$ 0
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	5,896
Amortized cost, troubled debt restructurings activity | $	$ 458	$ 929
Number of loans, troubled debt restructurings subsequent default | contract	1,562	3,972
Amortized cost, troubled debt restructurings subsequent default | $	$ 262	$ 675
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	677
Amortized cost, troubled debt restructurings activity | $	$ 26	$ 54
Number of loans, troubled debt restructurings subsequent default | contract	103	197
Amortized cost, troubled debt restructurings subsequent default | $	$ 8	$ 14
Adjustable-rate | Single-family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans, troubled debt restructurings activity | contract	37	78
Amortized cost, troubled debt restructurings activity | $	$ 6	$ 12
Number of loans, troubled debt restructurings subsequent default | contract	6	15
Amortized cost, troubled debt restructurings subsequent default | $	$ 1	$ 3
Other | Single-family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans, troubled debt restructurings activity | contract	174	328
Amortized cost, troubled debt restructurings activity | $	$ 17	$ 35
Number of loans, troubled debt restructurings subsequent default | contract	211	493
Amortized cost, troubled debt restructurings subsequent default | $	$ 38	$ 91