Mortgage Loans TDRs (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) contracts	Sep. 30, 2019 USD ($) contracts	Sep. 30, 2020 USD ($) contracts	Sep. 30, 2019 USD ($) contracts
Financing Receivable, Troubled Debt Restructuring [Line Items]
Average term extension of a single-family modified loan	159 months	164 months	166 months	160 months
Average interest rate reduction of a single-family modified loan	0.42%	0.15%	0.35%	0.11%
Number of loans troubled debt restructurings activity | contracts	7,052	12,024	29,667	38,518
Recorded investment troubled debt restructurings activity | $	$ 1,119	$ 1,910	$ 4,875	$ 5,994
Number of loans troubled debt restructurings subsequent default | contracts	3,199	4,203	12,748	13,909
Recorded investment troubled debt restructurings subsequent default | $	$ 568	$ 659	$ 2,324	$ 2,129
Single-family [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts	7,052	12,021	29,667	38,509
Recorded investment troubled debt restructurings activity | $	$ 1,119	$ 1,906	$ 4,875	$ 5,957
Number of loans troubled debt restructurings subsequent default | contracts	3,199	4,202	12,744	13,907
Recorded investment troubled debt restructurings subsequent default | $	$ 568	$ 646	$ 2,308	$ 2,110
Multifamily [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts	0	3	0	9
Recorded investment troubled debt restructurings activity | $	$ 0	$ 4	$ 0	$ 37
Number of loans troubled debt restructurings subsequent default | contracts	0	1	4	2
Recorded investment troubled debt restructurings subsequent default | $	$ 0	$ 13	$ 16	$ 19
FixedRateResidentialMortgage15yearMember | Single-family [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts	579	1,078	2,448	3,554
Recorded investment troubled debt restructurings activity | $	$ 50	$ 97	$ 216	$ 317
Number of loans troubled debt restructurings subsequent default | contracts	21	164	106	415
Recorded investment troubled debt restructurings subsequent default | $	$ 1	$ 12	$ 7	$ 30
Other [Member] | Single-family [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts	371	648	1,464	2,383
Recorded investment troubled debt restructurings activity | $	$ 47	$ 87	$ 185	$ 323
Number of loans troubled debt restructurings subsequent default | contracts	219	422	1,094	1,564
Recorded investment troubled debt restructurings subsequent default | $	$ 35	$ 62	$ 180	$ 247
Adjustable Rate Residential Mortgage [Member] | Single-family [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts	109	182	395	612
Recorded investment troubled debt restructurings activity | $	$ 16	$ 28	$ 62	$ 91
Number of loans troubled debt restructurings subsequent default | contracts	3	34	15	57
Recorded investment troubled debt restructurings subsequent default | $	$ 0	$ 5	$ 2	$ 8
Fixed Rate Residential Mortgage | Single-family [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts	5,993	10,113	25,360	31,960
Recorded investment troubled debt restructurings activity | $	$ 1,006	$ 1,694	$ 4,412	$ 5,226
Number of loans troubled debt restructurings subsequent default | contracts	2,956	3,582	11,529	11,871
Recorded investment troubled debt restructurings subsequent default | $	$ 532	$ 567	$ 2,119	$ 1,825