Mortgage Loans TDRs (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) contracts	Mar. 31, 2018 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Average term extension of a single-family modified loan	157 months	144 months
Average interest rate reduction of a single-family modified loan	0.10%	0.31%
Number of loans troubled debt restructurings activity | contracts	13,896	44,362
Recorded investment troubled debt restructurings activity | $	$ 2,112	$ 6,937
Single-family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	13,893	44,354
Recorded investment troubled debt restructurings activity | $	$ 2,099	$ 6,895
Single-family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	12,957	41,679
Recorded investment troubled debt restructurings activity | $	$ 1,971	$ 6,524
Single-family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	23	48
Recorded investment troubled debt restructurings activity | $	$ 4	$ 4
Single-family [Member] | Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	766	2,182
Recorded investment troubled debt restructurings activity | $	$ 97	$ 283
Single-family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	147	445
Recorded investment troubled debt restructurings activity | $	$ 27	$ 84
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	3	8
Recorded investment troubled debt restructurings activity | $	$ 13	$ 42