Mortgage Loans Aging (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 72,225	$ 79,592
Current	2,990,685	2,956,120
Total recorded investment in loans	3,062,910	3,035,712
Recorded investment in loans 90 days or more delinquent and accruing interest	296	349
Recorded investment in nonaccrual loans	42,027	44,846
30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	34,927	34,814
60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	9,109	9,717
Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	28,189	35,061
Single-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	72,037	79,446
Current	2,766,768	2,756,092
Total recorded investment in loans	2,838,805	2,835,538
Recorded investment in loans 90 days or more delinquent and accruing interest	296	349
Recorded investment in nonaccrual loans	$ 41,529	$ 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 Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 34,902	$ 34,791
Single-family [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	9,109	9,717
Single-family [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	28,026	34,938
Single-family [Member] | Primary [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	58,747	63,437
Current	2,625,085	2,598,756
Total recorded investment in loans	2,683,832	2,662,193
Recorded investment in loans 90 days or more delinquent and accruing interest	24	46
Recorded investment in nonaccrual loans	32,806	34,216
Single-family [Member] | Primary [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	29,741	29,154
Single-family [Member] | Primary [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	7,505	7,937
Single-family [Member] | Primary [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	21,501	26,346
Single-family [Member] | Government [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	341	373
Current	37,698	40,461
Total recorded investment in loans	38,039	40,834
Recorded investment in loans 90 days or more delinquent and accruing interest	264	291
Recorded investment in nonaccrual loans	0	0
Single-family [Member] | Government [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	54	58
Single-family [Member] | Government [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	23	24
Single-family [Member] | Government [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	264	291
Single-family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	9,444	11,498
Current	76,207	84,603
Total recorded investment in loans	85,651	96,101
Recorded investment in loans 90 days or more delinquent and accruing interest	2	6
Recorded investment in nonaccrual loans	6,386	7,407
Single-family [Member] | Alt-A [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	3,706	4,085
Single-family [Member] | Alt-A [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	1,131	1,272
Single-family [Member] | Alt-A [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	4,607	6,141
Single-family [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	3,505	4,138
Current	27,778	32,272
Total recorded investment in loans	31,283	36,410
Recorded investment in loans 90 days or more delinquent and accruing interest	6	6
Recorded investment in nonaccrual loans	2,337	2,632
Single-family [Member] | Other [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	1,401	1,494
Single-family [Member] | Other [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	450	484
Single-family [Member] | Other [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	1,654	2,160
Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	188	146
Current	223,917	200,028
Total recorded investment in loans	224,105	200,174
Recorded investment in loans 90 days or more delinquent and accruing interest	0	0
Recorded investment in nonaccrual loans	$ 498	$ 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 Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 25	$ 23
Multifamily [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 163	$ 123