Equity Narratives (Details)			12 Months Ended
	Sep. 08, 2008 USD ($) $ / shares shares	Sep. 08, 2008 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	Mar. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2013 USD ($)	Sep. 07, 2008 $ / shares
Class of Stock [Line Items]
Preferred Stock, Redemption Terms			P2Y
Common Stock, Shares, Outstanding | shares			1,200,000,000	1,158,087,567
Comprehensive Income (Loss), Net of Tax, Attributable to Parent			$ 13,969,000,000	$ 15,611,000,000	$ 2,257,000,000
Reduction in Dividends Paid				2,400,000,000
Preferred Stock, Covenant, Maximum Mortgage Assets			153,600,000,000	250,000,000,000
Payment Of Cash Dividends On Senior Preferred Stock To Treasury			$ 5,601,000,000	$ 9,372,000,000	12,015,000,000
Convertible Series 2004-1 Preferred Stock [Member]
Class of Stock [Line Items]
Conversion price per share | $ / shares			$ 94.31
Conversion rate			1,060.3329
Preferred Stock, Redemption Price Per Share | $ / shares			$ 105,000
Series 2008-2 Senior Preferred Stock [Member]
Class of Stock [Line Items]
Senior Preferred Stock, Par or Stated Value Per Share | $ / shares	$ 1,000	$ 1,000	$ 120,836
Shares of variable liquidation preference senior preferred stock issued | shares	1,000,000
Aggregate liquidation preference of senior preferred stock	$ 1,000,000,000.0	$ 1,000,000,000.0
Value assigned to Treasury's commitment and recorded as a reduction to additional paid-in-capital		$ 4,500,000,000
Preferred Stock Covenant Maximum Fair Market Value of assets and properties per transaction			$ 250,000,000
Preferred Stock, Covenant, Current Period Debt v.s. Maximum Mortgage Assets Allowed at Prior Year End, Maximum Ratio				120.00%
Minimum [Member] | Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Redemption Price Per Share | $ / shares			$ 50
Maximum [Member] | Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Redemption Price Per Share | $ / shares			$ 52.50
US Treasury [Member]
Class of Stock [Line Items]
Percentage Of Common Shares Attributable to Warrants Issued to Treasury as Percentage to Total Diluted Common Shares			79.90%
Aggregate liquidation preference of senior preferred stock			$ 131,200,000,000
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement			119,800,000,000
Capital Reserve Amount Fiscal Year Senior Preferred Stock Purchase Agreement September 2019 Amendment								$ 22,000,000,000
Capital reserve amount for the fiscal year based on the amended Senior Preferred Stock Purchase agreement				$ 3,000,000,000.0				$ 25,000,000,000	$ 3,000,000,000	$ 0	$ 0
Annual Reduction of Capital Reserve Amount from 2013 to 2017, Senior Preferred Stock Purchase Agreement, Amendment				600,000,000	$ 600,000,000
Common stock warrant exercise price per share | $ / shares												$ 0.00001
Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement			113,900,000,000
Fannie Mae [Member]
Class of Stock [Line Items]
Debt Instrument, Face Amount			$ 182,200,000,000	$ 232,500,000,000
Forecast [Member]
Class of Stock [Line Items]
Preferred Stock, Covenant, Maximum Mortgage Assets							$ 225,000,000,000
Debt Instrument, Face Amount							$ 300,000,000,000
Forecast [Member] | US Treasury [Member]
Class of Stock [Line Items]
Aggregate liquidation preference of senior preferred stock						$ 135,400,000,000