Mortgage Loans TDR (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) contracts	Sep. 30, 2014 USD ($) contracts	Sep. 30, 2015 USD ($) contracts	Sep. 30, 2014 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Average term extension of a single-family modified loan	159 months	162 months	161 months	161 months
Average interest rate reduction of a single-family modified loan	0.69%	0.89%	0.75%	1.04%
Number of loans troubled debt restructurings activity | contracts	17,112	27,028	63,063	90,950
Recorded investment troubled debt restructurings activity	$ 2,362	$ 4,756	$ 8,847	$ 14,241
Number of loans troubled debt restructurings subsequent default | contracts	8,258	10,647	23,907	31,240
Recorded investment troubled debt restructurings subsequent default	$ 1,254	$ 1,664	$ 3,611	$ 4,961
Single-family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	17,109	27,021	63,056	90,934
Recorded investment troubled debt restructurings activity	$ 2,352	$ 3,945	$ 8,831	$ 13,392
Number of loans troubled debt restructurings subsequent default | contracts	8,258	10,646	23,904	31,234
Recorded investment troubled debt restructurings subsequent default	$ 1,254	$ 1,659	$ 3,605	$ 4,939
Single-family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	14,926	23,057	54,284	76,831
Recorded investment troubled debt restructurings activity	$ 2,021	$ 3,270	$ 7,443	$ 10,944
Number of loans troubled debt restructurings subsequent default | contracts	6,847	8,798	19,726	25,586
Recorded investment troubled debt restructurings subsequent default	$ 1,003	$ 1,312	$ 2,870	$ 3,873
Single-family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	54	91	192	264
Recorded investment troubled debt restructurings activity	$ 6	$ 12	$ 22	$ 33
Number of loans troubled debt restructurings subsequent default | contracts	31	38	88	74
Recorded investment troubled debt restructurings subsequent default	$ 3	$ 6	$ 12	$ 9
Single-family [Member] | Alt-A
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	1,805	3,175	7,127	11,231
Recorded investment troubled debt restructurings activity	$ 268	$ 521	$ 1,101	$ 1,875
Number of loans troubled debt restructurings subsequent default | contracts	1,052	1,372	3,168	4,212
Recorded investment troubled debt restructurings subsequent default	$ 183	$ 241	$ 537	$ 753
Single-family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	324	698	1,453	2,608
Recorded investment troubled debt restructurings activity	$ 57	$ 142	$ 265	$ 540
Number of loans troubled debt restructurings subsequent default | contracts	328	438	922	1,362
Recorded investment troubled debt restructurings subsequent default	$ 65	$ 100	$ 186	$ 304
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	3	7	7	16
Recorded investment troubled debt restructurings activity	$ 10	$ 811	$ 16	$ 849
Number of loans troubled debt restructurings subsequent default | contracts	0	1	3	6
Recorded investment troubled debt restructurings subsequent default	$ 0	$ 5	$ 6	$ 22