Mortgage Loans TDRs (Details) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019 USD ($) contracts	Dec. 31, 2018 USD ($) contracts	Dec. 31, 2017 USD ($) contracts
Financing Receivable, Troubled Debt Restructuring [Line Items]
Average term extension of a single-family modified loan	162 months		109 months	153 months
Average interest rate reduction of a single-family modified loan		0.13%	0.21%	0.56%
Number of loans troubled debt restructurings activity | contracts		51,870	95,826	66,414
Recorded investment troubled debt restructurings activity | $		$ 8,146	$ 14,427	$ 9,342
Single-Family [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts		51,859	95,812	66,406
Recorded investment troubled debt restructurings activity | $		$ 8,090	$ 14,353	$ 9,243
Single-Family [Member] | Primary [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts		48,858	89,192	59,708
Recorded investment troubled debt restructurings activity | $		$ 7,688	$ 13,437	$ 8,247
Single-Family [Member] | Government [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts		72	115	171
Recorded investment troubled debt restructurings activity | $		$ 8	$ 11	$ 18
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts		2,465	5,378	5,369
Recorded investment troubled debt restructurings activity | $		$ 313	$ 697	$ 771
Single-Family [Member] | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts		464	1,127	1,158
Recorded investment troubled debt restructurings activity | $		$ 81	$ 208	$ 207
Multifamily [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans troubled debt restructurings activity | contracts		11	14	8
Recorded investment troubled debt restructurings activity | $		$ 56	$ 74	$ 99