Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ (19,084)	$ (23,465)
Benefit (provision) for loan losses	(58)	411
Charge-offs	469	1,040
Recoveries	(60)	(85)
Other	(1)	(30)
Ending balance	(18,734)	(22,129)
Single-family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(18,849)	(23,283)
Benefit (provision) for loan losses	(78)	420
Charge-offs	465	1,040
Recoveries	(60)	(85)
Other	(1)	(30)
Ending balance	(18,523)	(21,938)
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(235)	(182)
Benefit (provision) for loan losses	20	(9)
Charge-offs	4	0
Ending balance	$ (211)	$ (191)