Mortgage Loans Aging (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	$ 34,814	$ 34,867
60 - 89 days delinquent	9,717	10,352
Seriously delinquent	35,061	54,008
Total delinquent	79,592	99,227
Current	2,956,120	2,948,567
Total recorded investment in loans	3,035,712	3,047,794
Recorded investment in loans 90 days or more delinquent and accruing interest	349	374
Recorded investment in nonaccrual loans	44,846	64,645
Single-Family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	34,791	34,807
60 - 89 days delinquent	9,717	10,352
Seriously delinquent	34,938	53,919
Total delinquent	79,446	99,078
Current	2,756,092	2,759,483
Total recorded investment in loans	2,835,538	2,858,561
Recorded investment in loans 90 days or more delinquent and accruing interest	349	374
Recorded investment in nonaccrual loans	$ 44,255	$ 63,822
Single-Family [Member] | Minimum [Member]
Table Footnote [Abstract]
Serious delinquency: days past due	90 days	90 days
Single-Family [Member] | Primary [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	$ 29,154	$ 29,130
60 - 89 days delinquent	7,937	8,396
Seriously delinquent	26,346	38,248
Total delinquent	63,437	75,774
Current	2,598,756	2,580,446
Total recorded investment in loans	2,662,193	2,656,220
Recorded investment in loans 90 days or more delinquent and accruing interest	46	55
Recorded investment in nonaccrual loans	34,216	46,556
Single-Family [Member] | Government [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	58	63
60 - 89 days delinquent	24	26
Seriously delinquent	291	305
Total delinquent	373	394
Current	40,461	44,927
Total recorded investment in loans	40,834	45,321
Recorded investment in loans 90 days or more delinquent and accruing interest	291	305
Recorded investment in nonaccrual loans	0	0
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	4,085	4,094
60 - 89 days delinquent	1,272	1,414
Seriously delinquent	6,141	11,603
Total delinquent	11,498	17,111
Current	84,603	95,650
Total recorded investment in loans	96,101	112,761
Recorded investment in loans 90 days or more delinquent and accruing interest	6	8
Recorded investment in nonaccrual loans	7,407	13,007
Single-Family [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	1,494	1,520
60 - 89 days delinquent	484	516
Seriously delinquent	2,160	3,763
Total delinquent	4,138	5,799
Current	32,272	38,460
Total recorded investment in loans	36,410	44,259
Recorded investment in loans 90 days or more delinquent and accruing interest	6	6
Recorded investment in nonaccrual loans	2,632	4,259
Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	23	60
Seriously delinquent	123	89
Total delinquent	146	149
Current	200,028	189,084
Total recorded investment in loans	200,174	189,233
Recorded investment in loans 90 days or more delinquent and accruing interest	0	0
Recorded investment in nonaccrual loans	$ 591	$ 823
Multifamily [Member] | Minimum [Member]
Table Footnote [Abstract]
Serious delinquency: days past due	60 days	60 days
Multifamily [Member] | Maximum [Member]
Table Footnote [Abstract]
Serious delinquency: days past due	89 days	89 days