Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 22,129	$ 25,819	$ 23,465	$ 27,951
Benefit for loan losses	(1,196)	(1,336)	(1,607)	(2,368)
Charge-offs	(689)	(821)	(1,729)	(2,105)
Recoveries	147	115	232	235
Other	8	22	38	86
Ending balance	20,399	23,799	20,399	23,799
Single-family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	21,938	25,597	23,283	27,709
Benefit for loan losses	(1,185)	(1,332)	(1,605)	(2,348)
Charge-offs	(689)	(818)	(1,729)	(2,097)
Recoveries	146	115	231	234
Other	8	22	38	86
Ending balance	20,218	23,584	20,218	23,584
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	191	222	182	242
Benefit for loan losses	(11)	(4)	(2)	(20)
Charge-offs	0	(3)	0	(8)
Recoveries	1	0	1	1
Ending balance	$ 181	$ 215	$ 181	$ 215