Mortgage Loans Aging (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 58,821	$ 60,485
Current	3,203,995	3,194,683
Total recorded investment in loans	3,262,816	3,255,168
Recorded investment in loans 90 days or more delinquent and accruing interest	190	195
Recorded investment in nonaccrual loans	30,297	30,872
30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	32,913	33,720
60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	8,497	9,002
Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	17,411	17,763
Single-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	58,625	60,258
Current	2,899,794	2,899,246
Total recorded investment in loans	2,958,419	2,959,504
Recorded investment in loans 90 days or more delinquent and accruing interest	190	195
Recorded investment in nonaccrual loans	29,788	$ 30,380
Table Footnote [Abstract]
Mortgage Loans in Process of Foreclosure, Amount	$ 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, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 32,910	$ 33,664
Single-family [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	8,497	9,002
Single-family [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	17,218	17,592
Single-family [Member] | Primary [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	51,618	53,218
Current	2,821,187	2,816,047
Total recorded investment in loans	2,872,805	2,869,265
Recorded investment in loans 90 days or more delinquent and accruing interest	24	22
Recorded investment in nonaccrual loans	25,710	26,170
Single-family [Member] | Primary [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	29,620	30,471
Single-family [Member] | Primary [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	7,397	7,881
Single-family [Member] | Primary [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	14,601	14,866
Single-family [Member] | Government [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	226	243
Current	20,901	21,887
Total recorded investment in loans	21,127	22,130
Recorded investment in loans 90 days or more delinquent and accruing interest	162	169
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	48	57
Single-family [Member] | Government [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	16	17
Single-family [Member] | Government [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	162	169
Single-family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	5,052	4,997
Current	45,750	48,274
Total recorded investment in loans	50,802	53,271
Recorded investment in loans 90 days or more delinquent and accruing interest	1	2
Recorded investment in nonaccrual loans	2,998	3,082
Single-family [Member] | Alt-A [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	2,470	2,332
Single-family [Member] | Alt-A [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	803	821
Single-family [Member] | Alt-A [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	1,779	1,844
Single-family [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	1,729	1,800
Current	11,956	13,038
Total recorded investment in loans	13,685	14,838
Recorded investment in loans 90 days or more delinquent and accruing interest	3	2
Recorded investment in nonaccrual loans	1,080	1,128
Single-family [Member] | Other [Member] | 30 to 59 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	772	804
Single-family [Member] | Other [Member] | 60 to 89 Days Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	281	283
Single-family [Member] | Other [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	676	713
Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	196	227
Current	304,201	295,437
Total recorded investment in loans	304,397	295,664
Recorded investment in loans 90 days or more delinquent and accruing interest	0	0
Recorded investment in nonaccrual loans	$ 509	$ 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, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 3	$ 56
Multifamily [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent	$ 193	$ 171