Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ (16,812)	$ (20,399)	$ (19,084)	$ (23,465)
Benefit for loan losses	710	(205)	1,922	1,402
Charge-offs	509	437	1,710	2,166
Recoveries	(68)	(44)	(192)	(276)
Other	(2)	17	(19)	(21)
Ending balance	(15,663)	(20,194)	(15,663)	(20,194)
Single-family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(16,602)	(20,218)	(18,849)	(23,283)
Benefit for loan losses	724	(163)	1,916	1,442
Charge-offs	509	434	1,705	2,163
Recoveries	(65)	(42)	(189)	(273)
Other	(2)	17	(19)	(21)
Ending balance	(15,436)	(19,972)	(15,436)	(19,972)
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(210)	(181)	(235)	(182)
Benefit for loan losses	(14)	(42)	6	(40)
Charge-offs	0	3	5	3
Recoveries	(3)	(2)	(3)	(3)
Ending balance	$ (227)	$ (222)	$ (227)	$ (222)