Mortgage Loans TDRs with Sub Defaults (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) contracts	Dec. 31, 2015 USD ($) contracts	Dec. 31, 2014 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	25,043	31,684	41,116
Recorded investment troubled debt restructurings subsequent default | $	$ 3,667	$ 4,783	$ 6,499
Single-Family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	25,038	31,681	41,107
Recorded investment troubled debt restructurings subsequent default | $	$ 3,621	$ 4,777	$ 6,457
Single-Family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	20,810	26,206	33,853
Recorded investment troubled debt restructurings subsequent default | $	$ 2,938	$ 3,808	$ 5,095
Single-Family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	95	118	124
Recorded investment troubled debt restructurings subsequent default | $	$ 11	$ 16	$ 15
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	3,131	4,128	5,392
Recorded investment troubled debt restructurings subsequent default | $	$ 500	$ 706	$ 960
Single-Family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	1,002	1,229	1,738
Recorded investment troubled debt restructurings subsequent default | $	$ 172	$ 247	$ 387
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	5	3	9
Recorded investment troubled debt restructurings subsequent default | $	$ 46	$ 6	$ 42