Mortgage Loans Aging (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Days delinquent	$ 55,004	$ 60,485
Current	3,256,694	3,194,683
Total recorded investment in loans	3,311,698	3,255,168
Recorded investment in loans 90 days or more delinquent and accruing interest	173	195
Recorded investment in nonaccrual loans	27,472	30,872
30 to 59 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	31,576	33,720
60 to 89 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	8,011	9,002
Seriously Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	15,417	17,763
Single-family [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	54,791	60,258
Current	2,935,710	2,899,246
Total recorded investment in loans	2,990,501	2,959,504
Recorded investment in loans 90 days or more delinquent and accruing interest	173	195
Recorded investment in nonaccrual loans	26,868	30,380
Table Footnote [Abstract]
Mortgage Loans in Process of Foreclosure, Amount	$ 8,200	$ 10,100
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, Past Due [Line Items]
Days delinquent	$ 31,544	$ 33,664
Single-family [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	8,011	9,002
Single-family [Member] | Seriously Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	15,236	17,592
Single-family [Member] | Primary [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	49,690	53,218
Current	2,867,330	2,816,047
Total recorded investment in loans	2,917,020	2,869,265
Recorded investment in loans 90 days or more delinquent and accruing interest	26	22
Recorded investment in nonaccrual loans	23,840	26,170
Single-family [Member] | Primary [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	29,211	30,471
Single-family [Member] | Primary [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	7,188	7,881
Single-family [Member] | Primary [Member] | Seriously Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	13,291	14,866
Single-family [Member] | Government [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	208	243
Current	17,881	21,887
Total recorded investment in loans	18,089	22,130
Recorded investment in loans 90 days or more delinquent and accruing interest	144	169
Recorded investment in nonaccrual loans	0	0
Single-family [Member] | Government [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	44	57
Single-family [Member] | Government [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	20	17
Single-family [Member] | Government [Member] | Seriously Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	144	169
Single-family [Member] | Alt-A
Financing Receivable, Past Due [Line Items]
Days delinquent	3,624	4,997
Current	40,663	48,274
Total recorded investment in loans	44,287	53,271
Recorded investment in loans 90 days or more delinquent and accruing interest	1	2
Recorded investment in nonaccrual loans	2,228	3,082
Single-family [Member] | Alt-A | 30 to 59 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	1,717	2,332
Single-family [Member] | Alt-A | 60 to 89 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	591	821
Single-family [Member] | Alt-A | Seriously Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	1,316	1,844
Single-family [Member] | Other [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	1,269	1,800
Current	9,836	13,038
Total recorded investment in loans	11,105	14,838
Recorded investment in loans 90 days or more delinquent and accruing interest	2	2
Recorded investment in nonaccrual loans	800	1,128
Single-family [Member] | Other [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	572	804
Single-family [Member] | Other [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	212	283
Single-family [Member] | Other [Member] | Seriously Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	485	713
Multifamily [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	213	227
Current	320,984	295,437
Total recorded investment in loans	321,197	295,664
Recorded investment in loans 90 days or more delinquent and accruing interest	0	0
Recorded investment in nonaccrual loans	$ 604	$ 492
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, Past Due [Line Items]
Days delinquent	$ 32	$ 56
Multifamily [Member] | Seriously Delinquent [Member]
Financing Receivable, Past Due [Line Items]
Days delinquent	$ 181	$ 171