Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2015
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ (23,465)	$ (27,951)	$ (35,541)
Benefit (provision) for loan losses	1,941	1,759	158
Charge-offs	2,798	3,266	9,774
Recoveries	(329)	(449)	(1,140)
Other	(29)	(90)	(1,202)
Ending balance	(19,084)	(23,465)	(27,951)
Natural Disasters and Other Casualty Events [Member]
Allowance for Loan Losses [Roll Forward]
Benefit (provision) for loan losses	900
Single-Family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(23,283)	(27,709)	(35,177)
Benefit (provision) for loan losses	1,994	1,704	68
Charge-offs	2,795	3,254	9,731
Recoveries	(326)	(442)	(1,136)
Other	(29)	(90)	(1,195)
Ending balance	(18,849)	(23,283)	(27,709)
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(182)	(242)	(364)
Benefit (provision) for loan losses	(53)	55	90
Charge-offs	3	12	43
Recoveries	(3)	(7)	(4)
Other	0	0	(7)
Ending balance	$ (235)	$ (182)	$ (242)
Change in Accounting Method Accounted for as Change in Estimate [Member]
Table Footnote [Abstract]
Advisory Bulletin impact for HFI loans				$ 1,800
Advisory Bulletin impact for preforeclosure property taxes and insurance receivable				724
Nonaccrual Policy [Member]
Table Footnote [Abstract]
Allowance for accrued interest receivables: charge-offs				$ 1,100