Mortgage Loans TDR (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) contracts	Jun. 30, 2014 USD ($) contracts	Jun. 30, 2015 USD ($) contracts	Jun. 30, 2014 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Average term extension of a single-family modified loan	162 months	162 months	162 months	161 months
Average interest rate reduction of a single-family modified loan	0.77%	0.99%	0.77%	1.12%
Number of loans troubled debt restructurings activity | contracts	21,088	29,578	45,951	63,922
Recorded investment troubled debt restructurings activity	$ 2,981	$ 4,374	$ 6,485	$ 9,485
Number of loans troubled debt restructurings subsequent default | contracts	7,447	10,025	15,649	20,593
Recorded investment troubled debt restructurings subsequent default	$ 1,078	$ 1,596	$ 2,357	$ 3,297
Single-family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	21,087	29,575	45,947	63,913
Recorded investment troubled debt restructurings activity	$ 2,980	$ 4,370	$ 6,479	$ 9,447
Number of loans troubled debt restructurings subsequent default | contracts	7,446	10,024	15,646	20,588
Recorded investment troubled debt restructurings subsequent default	$ 1,076	$ 1,593	$ 2,351	$ 3,280
Single-family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	17,951	24,932	39,358	53,774
Recorded investment troubled debt restructurings activity	$ 2,477	$ 3,564	$ 5,422	$ 7,674
Number of loans troubled debt restructurings subsequent default | contracts	6,156	8,190	12,879	16,788
Recorded investment troubled debt restructurings subsequent default	$ 864	$ 1,251	$ 1,867	$ 2,561
Single-family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	64	111	138	173
Recorded investment troubled debt restructurings activity	$ 8	$ 13	$ 16	$ 21
Number of loans troubled debt restructurings subsequent default | contracts	37	18	57	36
Recorded investment troubled debt restructurings subsequent default	$ 6	$ 1	$ 9	$ 3
Single-family [Member] | Alt-A
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	2,533	3,660	5,322	8,056
Recorded investment troubled debt restructurings activity	$ 395	$ 614	$ 833	$ 1,354
Number of loans troubled debt restructurings subsequent default | contracts	963	1,396	2,116	2,840
Recorded investment troubled debt restructurings subsequent default	$ 151	$ 252	$ 354	$ 512
Single-family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	539	872	1,129	1,910
Recorded investment troubled debt restructurings activity	$ 100	$ 179	$ 208	$ 398
Number of loans troubled debt restructurings subsequent default | contracts	290	420	594	924
Recorded investment troubled debt restructurings subsequent default	$ 55	$ 89	$ 121	$ 204
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	1	3	4	9
Recorded investment troubled debt restructurings activity	$ 1	$ 4	$ 6	$ 38
Number of loans troubled debt restructurings subsequent default | contracts	1	1	3	5
Recorded investment troubled debt restructurings subsequent default	$ 2	$ 3	$ 6	$ 17