Summary of Significant Accounting Policies Related Parties (Details) - USD ($)			3 Months Ended									12 Months Ended
	Dec. 30, 2016	Sep. 08, 2008	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2013	Sep. 07, 2008
Related Parties [Line Items]
Number of days after which we have not been paying debts or liabilities exceed assets FHFA must place us into receivership												60 days
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement				$ 116,100,000,000								$ 116,100,000,000
Payment Of Cash Dividends On Senior Preferred Stock To Treasury	$ 3,000,000,000											9,624,000,000	$ 10,278,000,000	$ 20,594,000,000
Net worth (deficit)				$ 6,071,000,000	$ 4,200,000,000			$ 4,059,000,000				$ 6,071,000,000	4,059,000,000	3,720,000,000			$ 9,591,000,000
Percentage of common shares attributable to warrants issued to Treasury as a percentage to total diluted common shares upon exercise of the right				79.90%								79.90%
Income taxes paid												$ 1,711,000,000	1,170,000,000	2,815,000,000
Unpaid principal balance guaranteed by a related party				$ 5,700,000,000								5,700,000,000
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees				$ 487,000,000	465,000,000	$ 453,000,000	$ 440,000,000	429,000,000	$ 413,000,000	$ 397,000,000	$ 382,000,000	$ 1,845,000,000	1,621,000,000	1,375,000,000
Basis Points of Each Dollar of Unpaid Principal Balance				420.00%								420.00%
Trading, at fair value				$ 40,562,000,000				39,908,000,000				$ 40,562,000,000	39,908,000,000
Interest Income recognized on Treasury Securities				128,000,000	$ 140,000,000	$ 128,000,000	$ 120,000,000	114,000,000	$ 99,000,000	$ 116,000,000	$ 115,000,000	516,000,000	444,000,000	553,000,000
Accrued interest receivable				7,737,000,000				7,726,000,000				7,737,000,000	7,726,000,000
U.S. Treasury Securities [Member]
Related Parties [Line Items]
Trading, at fair value				32,317,000,000				29,485,000,000				32,317,000,000	29,485,000,000
Scenario, Forecast [Member]
Related Parties [Line Items]
Undeclared Dividends On Senior Preferred Stock Next Quarter			$ 5,500,000,000
Series 2008-2 Senior Preferred Stock [Member]
Related Parties [Line Items]
Shares of variable liquidation preference senior preferred stock issued		1,000,000
Aggregate liquidation preference of senior preferred stock		$ 1,000,000,000
US Treasury [Member]
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement				116,100,000,000				116,100,000,000				116,100,000,000	116,100,000,000
Initial aggregate liquidation preference of senior preferred stock held by US Treasury				1,000,000,000								1,000,000,000
Aggregate liquidation preference of senior preferred stock				117,100,000,000								117,100,000,000
Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement				117,600,000,000								117,600,000,000
Capital reserve amount for the fiscal year based on the amended Senior Preferred Stock Purchase agreement				$ 1,200,000,000				1,800,000,000				$ 1,200,000,000	1,800,000,000
Percentage of common shares attributable to warrants issued to Treasury as a percentage to total diluted common shares upon exercise of the right				79.90%								79.90%						79.90%
Common stock warrant exercise price per share																		$ 0.00001
Fair value of the warrant at issuance		$ 3,500,000,000
Home Affordable Modification Program administrative expense reimbursements												$ 57,000,000	68,000,000	71,000,000
Income taxes paid												1,700,000,000	1,200,000,000	2,800,000,000
Interest Income, Related Party												$ 7,000,000
Income tax refund													277,000,000
Percentage of Initial Principal Loss Treasury Will Bear For the NIB Program				35.00%								35.00%
Basis Points Increase of Guarantee Fee Rate Resulting from the Temporary Payroll Tax Cut Continuation Act of 2011.				1000.00%								1000.00%
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees												$ 1,845,000,000	1,621,000,000	1,375,000,000
Recognized TCCA fees that had not been remitted to Treasury as of period end				$ 487,000,000				429,000,000				487,000,000	429,000,000
US Treasury [Member] | Other Expense [Member]
Related Parties [Line Items]
Affordable Housing Program Assessments												137,000,000	111,000,000
US Treasury [Member] | U.S. Treasury Securities [Member]
Related Parties [Line Items]
Trading, at fair value				32,300,000,000				29,500,000,000				32,300,000,000	29,500,000,000
Interest Income recognized on Treasury Securities												157,000,000	35,000,000	18,000,000
Accrued interest receivable				39,000,000				15,000,000				39,000,000	15,000,000
US Treasury [Member] | Scenario, Forecast [Member]
Related Parties [Line Items]
Capital reserve amount for the fiscal year based on the amended Senior Preferred Stock Purchase agreement															$ 0	$ 600,000,000
Freddie Mac [Member] | Freddie Mac [Member]
Related Parties [Line Items]
Fair value of mortgage-related securities				1,400,000,000				5,600,000,000				1,400,000,000	5,600,000,000
Accrued interest receivable				$ 5,000,000				$ 22,000,000				5,000,000	22,000,000
Investment income, interest												112,000,000	226,000,000	283,000,000
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees/expense												114,000,000	112,000,000	108,000,000
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire Equity Method Investments												$ 118,000,000	$ 66,000,000	$ 43,000,000