Mortgage Loans Aging (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	$ 74,222	$ 79,592
Current, recorded investment	3,021,594	2,956,120
Total recorded investment in loans	3,095,816	3,035,712
Recorded investment in loans 90 days or more delinquent and accruing interest	285	349
Recorded investment in nonaccrual loans	42,108	44,846
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	36,709	34,814
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	9,564	9,717
Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	27,949	35,061
Single-Family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	74,049	79,446
Current, recorded investment	2,789,886	2,756,092
Total recorded investment in loans	2,863,935	2,835,538
Recorded investment in loans 90 days or more delinquent and accruing interest	285	349
Recorded investment in nonaccrual loans	$ 41,705	$ 44,255
Single-Family [Member] | Minimum [Member]
Table Footnote [Abstract]
Serious delinquency: days past due	90 days	90 days
Single-Family [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	$ 36,665	$ 34,791
Single-Family [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	9,564	9,717
Single-Family [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	27,820	34,938
Single-Family [Member] | Primary [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	61,302	63,437
Current, recorded investment	2,654,195	2,598,756
Total recorded investment in loans	2,715,497	2,662,193
Recorded investment in loans 90 days or more delinquent and accruing interest	22	46
Recorded investment in nonaccrual loans	33,448	34,216
Single-Family [Member] | Primary [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	31,631	29,154
Single-Family [Member] | Primary [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	7,910	7,937
Single-Family [Member] | Primary [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	21,761	26,346
Single-Family [Member] | Government [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	334	373
Current, recorded investment	36,814	40,461
Total recorded investment in loans	37,148	40,834
Recorded investment in loans 90 days or more delinquent and accruing interest	256	291
Recorded investment in nonaccrual loans	0	0
Single-Family [Member] | Government [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	56	58
Single-Family [Member] | Government [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	22	24
Single-Family [Member] | Government [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	256	291
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	9,044	11,498
Current, recorded investment	72,903	84,603
Total recorded investment in loans	81,947	96,101
Recorded investment in loans 90 days or more delinquent and accruing interest	2	6
Recorded investment in nonaccrual loans	6,019	7,407
Single-Family [Member] | Alt-A [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	3,629	4,085
Single-Family [Member] | Alt-A [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	1,194	1,272
Single-Family [Member] | Alt-A [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	4,221	6,141
Single-Family [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	3,369	4,138
Current, recorded investment	25,974	32,272
Total recorded investment in loans	29,343	36,410
Recorded investment in loans 90 days or more delinquent and accruing interest	5	6
Recorded investment in nonaccrual loans	2,238	2,632
Single-Family [Member] | Other [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	1,349	1,494
Single-Family [Member] | Other [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	438	484
Single-Family [Member] | Other [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	1,582	2,160
Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	173	146
Current, recorded investment	231,708	200,028
Total recorded investment in loans	231,881	200,174
Recorded investment in loans 90 days or more delinquent and accruing interest	0	0
Recorded investment in nonaccrual loans	$ 403	$ 591
Multifamily [Member] | Minimum [Member]
Table Footnote [Abstract]
Serious delinquency: days past due	60 days	60 days
Multifamily [Member] | Maximum [Member]
Table Footnote [Abstract]
Serious delinquency: days past due	89 days	89 days
Multifamily [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	$ 44	$ 23
Multifamily [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	$ 129	$ 123