Consolidations and Transfers of Financial Assets Transfers of Financial Assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Transfers of Financial Assets [Line Items]
Unpaid principal balance portfolio securitizations	$ 228,500,000,000	$ 225,100,000,000	$ 118,500,000,000
Unconsolidated VIEs [Member]
Transfers of Financial Assets [Line Items]
Principal and interest received on retained interest	1,700,000,000	2,400,000,000	3,000,000,000
Unconsolidated VIEs [Member] | Fannie Mae Single-class MBS & Fannie Mae Megas [Member]
Transfers of Financial Assets [Line Items]
Unpaid principal balance	349,000,000	456,000,000
Fair value	383,000,000	504,000,000
Weighted-average coupon (percent)	6.21%	6.20%
Weighted-average loan age (years)	7 years 5 months	6 years 5 months
Weighted-average maturity (years)	21 years 6 months	22 years 6 months
Unconsolidated VIEs [Member] | REMICS & SMBS [Member]
Transfers of Financial Assets [Line Items]
Unpaid principal balance	6,899,000,000	8,667,000,000
Fair value	$ 7,959,000,000	$ 9,818,000,000
Weighted-average coupon (percent)	5.36%	5.53%
Weighted-average loan age (years)	5 years 5 months	4 years 7 months
Weighted-average maturity (years)	12 years 7 months	15 years 0 months