Short-Term Borrowings and Long-Term Debt Characteristics of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	$ 3,125,721	$ 3,115,583
Fannie Mae [Member]
Long-Term Debt [Line Items]
Face amount	389,400	464,600
Long-Term Debt by Year of Maturity [Abstract]
2016	52,829
2017	76,970
2018	60,555
2019	29,656
2020	30,129
Thereafter	64,989
Total long-term debt	315,128	355,431
Net unamortized discount, fair value adjustments and other cost basis adjustments	3,200	4,100
Fannie Mae [Member] | Zero-Coupon Debt [Member]
Long-Term Debt [Line Items]
Face amount	$ 82,100	$ 116,700
Effective interest rate	1.26%	0.77%
Fannie Mae [Member] | Callable [Member]
Long-Term Debt [Line Items]
Outstanding debt	$ 96,200	$ 115,000
Consolidated Trusts [Member]
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	2,810,593	$ 2,760,152
Earlier of Contractual Maturity or Next Call Date [Member]
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	3,125,721
Earlier of Contractual Maturity or Next Call Date [Member] | Fannie Mae [Member]
Long-Term Debt by Year of Maturity [Abstract]
2016	143,970
2017	69,351
2018	32,832
2019	19,036
2020	16,658
Thereafter	33,281
Total long-term debt	315,128
Earlier of Contractual Maturity or Next Call Date [Member] | Consolidated Trusts [Member]
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	$ 2,810,593