Mortgage Loans Aging (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 61,095	$ 74,222
Current	3,061,355	3,021,594
Total recorded investment in loans	3,122,450	3,095,816
Recorded investment in loans 90 days or more delinquent and accruing interest	263	285
Recorded investment in nonaccrual loans	37,718	42,108
30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	28,389	36,709
60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	7,861	9,564
Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	24,845	27,949
Single-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	60,956	74,049
Current	2,818,890	2,789,886
Total recorded investment in loans	2,879,846	2,863,935
Recorded investment in loans 90 days or more delinquent and accruing interest	263	285
Recorded investment in nonaccrual loans	$ 37,335	$ 41,705
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	$ 28,364	$ 36,665
Single-family [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	7,861	9,564
Single-family [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	24,731	27,820
Single-family [Member] | Primary [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	49,898	61,302
Current	2,688,070	2,654,195
Total recorded investment in loans	2,737,968	2,715,497
Recorded investment in loans 90 days or more delinquent and accruing interest	19	22
Recorded investment in nonaccrual loans	29,929	33,448
Single-family [Member] | Primary [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	24,067	31,631
Single-family [Member] | Primary [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	6,468	7,910
Single-family [Member] | Primary [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	19,363	21,761
Single-family [Member] | Government [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	300	334
Current	35,931	36,814
Total recorded investment in loans	36,231	37,148
Recorded investment in loans 90 days or more delinquent and accruing interest	237	256
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	47	56
Single-family [Member] | Government [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	16	22
Single-family [Member] | Government [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	237	256
Single-family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	7,878	9,044
Current	70,426	72,903
Total recorded investment in loans	78,304	81,947
Recorded investment in loans 90 days or more delinquent and accruing interest	2	2
Recorded investment in nonaccrual loans	5,421	6,019
Single-family [Member] | Alt-A [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	3,119	3,629
Single-family [Member] | Alt-A [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	1,006	1,194
Single-family [Member] | Alt-A [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	3,753	4,221
Single-family [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	2,880	3,369
Current	24,463	25,974
Total recorded investment in loans	27,343	29,343
Recorded investment in loans 90 days or more delinquent and accruing interest	5	5
Recorded investment in nonaccrual loans	1,985	2,238
Single-family [Member] | Other [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	1,131	1,349
Single-family [Member] | Other [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	371	438
Single-family [Member] | Other [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	1,378	1,582
Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	139	173
Current	242,465	231,708
Total recorded investment in loans	242,604	231,881
Recorded investment in loans 90 days or more delinquent and accruing interest	0	0
Recorded investment in nonaccrual loans	$ 383	$ 403
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	$ 44
Multifamily [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 114	$ 129