Consolidations and Transfers of Financial Assets Transfers of Financial Assets (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			12 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Unconsolidated VIEs [Member]	Jun. 30, 2012 Unconsolidated VIEs [Member]	Jun. 30, 2013 Unconsolidated VIEs [Member]	Jun. 30, 2012 Unconsolidated VIEs [Member]	Jun. 30, 2013 Unconsolidated VIEs [Member] Fannie Mae Single-class MBS & Fannie Mae Megas [Member]	Dec. 31, 2012 Unconsolidated VIEs [Member] Fannie Mae Single-class MBS & Fannie Mae Megas [Member]	Jun. 30, 2013 Unconsolidated VIEs [Member] REMICS & SMBS [Member]		Dec. 31, 2012 Unconsolidated VIEs [Member] REMICS & SMBS [Member]
Transfers of Financial Assets [Line Items]
Unpaid principal balance portfolio securitizations	$ 62,500,000,000	$ 46,400,000,000	$ 131,800,000,000	$ 88,100,000,000
Unpaid principal balance									396,000,000	456,000,000	7,804,000,000	[1]	8,667,000,000	[1]
Fair value									434,000,000	504,000,000	9,005,000,000	[1]	9,818,000,000	[1]
Weighted-average coupon									6.21%	6.20%	5.45%	[1]	5.53%	[1]
Weighted-average loan age									7 years 0 months	6 years 5 months	5 years 1 month	[1]	4 years 7 months	[1]
Weighted-average maturity									22 years 0 months	22 years 6 months	13 years 2 months	[1]	15 years 0 months	[1]
Principal and interest received on retained interest					$ 469,000,000	$ 636,000,000	$ 928,000,000	$ 1,300,000,000

[1] Consists of Real Estate Mortgage Investment Conduits (“REMICs”) and stripped mortgage-backed securities (“SMBS”).