Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ (14,203)	$ (19,084)	$ (23,465)
Benefit (provision) for loan losses	3,961	2,987	1,941
Charge-offs	1,307	2,152	2,798
Recoveries	(75)	(240)	(329)
Other	(6)	(18)	(29)
Ending balance	(9,016)	(14,203)	(19,084)
Single-Family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(13,969)	(18,849)	(23,283)
Benefit (provision) for loan losses	3,988	2,990	1,994
Charge-offs	1,299	2,148	2,795
Recoveries	(71)	(240)	(326)
Other	(6)	(18)	(29)
Ending balance	(8,759)	(13,969)	(18,849)
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(234)	(235)	(182)
Benefit (provision) for loan losses	(27)	(3)	(53)
Charge-offs	8	4	3
Recoveries	(4)	0	(3)
Ending balance	$ (257)	$ (234)	$ (235)