Mortgage Loans Individually Impaired Loans - 2 (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2019
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	$ 92,622	$ 95,166
Individually impaired loans with no related allowance recorded: total interest income recognized	310	580
Table Footnote [Abstract]
Individually impaired loans with related allowance recorded: total interest income recognized	966	1,989
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	86	181
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	42	73
Individually impaired loans with no related allowance recorded: average recorded investment	18,737	18,646
Impaired Financing Receivable, Average Recorded Investment	111,359	113,812
Individually impaired loans: total interest income recognized	1,276	2,569
Impaired Financing Receivable, Interest Income, Cash Basis Method	128	254
Single-family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	92,301	94,887
Individually impaired loans with no related allowance recorded: total interest income recognized	304	572
Table Footnote [Abstract]
Individually impaired loans with related allowance recorded: total interest income recognized	963	1,984
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	86	181
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	42	73
Individually impaired loans with no related allowance recorded: average recorded investment	18,340	18,266
Single-family [Member] \| Other [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	18,139	18,999
Individually impaired loans with no related allowance recorded: total interest income recognized	55	103
Table Footnote [Abstract]
Individually impaired loans with related allowance recorded: total interest income recognized	189	393
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	14	30
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	6	9
Individually impaired loans with no related allowance recorded: average recorded investment	2,870	2,934
Single-family [Member] \| FixedRateResidentialMortgage15yearMember
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	1,250	1,286
Individually impaired loans with no related allowance recorded: total interest income recognized	4	7
Table Footnote [Abstract]
Individually impaired loans with related allowance recorded: total interest income recognized	11	22
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	1	2
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	1	2
Individually impaired loans with no related allowance recorded: average recorded investment	308	313
Single-family [Member] \| Adjustable Rate Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	130	124
Individually impaired loans with no related allowance recorded: total interest income recognized	4	9
Table Footnote [Abstract]
Individually impaired loans with related allowance recorded: total interest income recognized	1	3
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	0	0
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	1	1
Individually impaired loans with no related allowance recorded: average recorded investment	359	379
Single-family [Member] \| Fixed Rate Residential Mortgage
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	72,782	74,478
Individually impaired loans with no related allowance recorded: total interest income recognized	241	453
Table Footnote [Abstract]
Individually impaired loans with related allowance recorded: total interest income recognized	762	1,566
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	71	149
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	34	61
Individually impaired loans with no related allowance recorded: average recorded investment	14,803	14,640
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	321	279
Individually impaired loans with no related allowance recorded: total interest income recognized	6	8
Table Footnote [Abstract]
Individually impaired loans with related allowance recorded: total interest income recognized	3	5
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	0	0
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	0	0
Individually impaired loans with no related allowance recorded: average recorded investment	$ 397	$ 380

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