Mortgage Loans TDR (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) contracts	Dec. 31, 2014 USD ($) contracts	Dec. 31, 2013 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Average term extension of a single-family modified loan	161 months	161 months	154 months
Average interest rate reduction of a single-family modified loan	0.74%	0.99%	1.68%
Number of loans troubled debt restructurings activity | contracts	82,418	119,412	155,040
Recorded investment troubled debt restructurings activity | $	$ 11,487	$ 18,328	$ 24,436
Number of loans troubled debt restructurings subsequent default | contracts	31,684	41,116	58,372
Recorded investment troubled debt restructurings subsequent default | $	$ 4,783	$ 6,499	$ 9,476
Single-Family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	82,406	119,393	155,007
Recorded investment troubled debt restructurings activity | $	$ 11,447	$ 17,475	$ 24,223
Number of loans troubled debt restructurings subsequent default | contracts	31,681	41,107	58,363
Recorded investment troubled debt restructurings subsequent default | $	$ 4,777	$ 6,457	$ 9,412
Single-Family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	71,293	100,956	126,998
Recorded investment troubled debt restructurings activity | $	$ 9,713	$ 14,301	$ 19,016
Number of loans troubled debt restructurings subsequent default | contracts	26,206	33,853	45,539
Recorded investment troubled debt restructurings subsequent default | $	$ 3,808	$ 5,095	$ 6,978
Single-Family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	241	365	312
Recorded investment troubled debt restructurings activity | $	$ 27	$ 47	$ 35
Number of loans troubled debt restructurings subsequent default | contracts	118	124	130
Recorded investment troubled debt restructurings subsequent default | $	$ 16	$ 15	$ 17
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	9,037	14,715	21,471
Recorded investment troubled debt restructurings activity | $	$ 1,374	$ 2,441	$ 3,794
Number of loans troubled debt restructurings subsequent default | contracts	4,128	5,392	9,601
Recorded investment troubled debt restructurings subsequent default | $	$ 706	$ 960	$ 1,732
Single-Family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	1,835	3,357	6,226
Recorded investment troubled debt restructurings activity | $	$ 333	$ 686	$ 1,378
Number of loans troubled debt restructurings subsequent default | contracts	1,229	1,738	3,093
Recorded investment troubled debt restructurings subsequent default | $	$ 247	$ 387	$ 685
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	12	19	33
Recorded investment troubled debt restructurings activity | $	$ 40	$ 853	$ 213
Number of loans troubled debt restructurings subsequent default | contracts	3	9	9
Recorded investment troubled debt restructurings subsequent default | $	$ 6	$ 42	$ 64