Summary of Significant Accounting Policies Related Parties (Details) - USD ($) $ / shares in Units, shares in Millions					3 Months Ended									12 Months Ended
	Jan. 01, 2018	Dec. 30, 2017	Dec. 29, 2017	Sep. 08, 2008	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2018	Dec. 31, 2014	Dec. 31, 2013	Sep. 07, 2008
Related Parties [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%													35.00%	35.00%	35.00%
Convertible preferred stock									131
Weighted-average shares of common stock that would be issued upon the full exercise of the warrant issued to Treasury													4,600	4,600	4,600	4,600
Number of days after which we have not been paying debts or liabilities exceed assets FHFA must place us into receivership														60 days
Net worth (deficit)					$ (3,686,000,000)	$ 3,600,000,000			$ 6,071,000,000				$ 4,059,000,000	$ (3,686,000,000)	$ 6,071,000,000	$ 4,059,000,000		$ 3,720,000,000
Payment Of Cash Dividends On Senior Preferred Stock To Treasury			$ 648,000,000											$ 12,015,000,000	9,624,000,000	10,278,000,000
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														$ 3,090,000,000	1,711,000,000	1,170,000,000
Unpaid principal balance guaranteed by a related party					$ 4,800,000,000									4,800,000,000
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees					$ (544,000,000)	(531,000,000)	$ (518,000,000)	$ (503,000,000)	(487,000,000)	$ (465,000,000)	$ (453,000,000)	$ (440,000,000)		$ (2,096,000,000)	(1,845,000,000)	(1,621,000,000)
Basis Points of Each Dollar of Unpaid Principal Balance					420.00%									420.00%
Trading, at fair value					$ 34,679,000,000				40,562,000,000					$ 34,679,000,000	40,562,000,000
Interest Income recognized on Treasury Securities					193,000,000	195,000,000	$ 176,000,000	$ 142,000,000	128,000,000	$ 140,000,000	$ 128,000,000	$ 120,000,000		706,000,000	516,000,000	444,000,000
Accrued interest receivable					8,133,000,000				7,737,000,000					8,133,000,000	7,737,000,000
U.S. Treasury Securities [Member]
Related Parties [Line Items]
Trading, at fair value					29,222,000,000				32,317,000,000					29,222,000,000	32,317,000,000
Series 2008-2 Senior Preferred Stock [Member]
Related Parties [Line Items]
Shares of variable liquidation preference senior preferred stock issued				1
Aggregate liquidation preference of senior preferred stock				$ 1,000,000,000
Payment Of Cash Dividends On Senior Preferred Stock To Treasury		$ 648,000,000
US Treasury [Member]
Related Parties [Line Items]
Reduction in Dividends Paid					2,400,000,000									2,400,000,000
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
Aggregate liquidation preference of senior preferred stock					120,100,000,000									120,100,000,000
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	$ 0				$ 600,000,000	$ 600,000,000			1,200,000,000					$ 600,000,000	1,200,000,000				$ 3,000,000,000
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														$ 40,000,000	57,000,000	68,000,000
Interest Income, Related Party														$ 51,000,000	7,000,000
Income tax refund															1,500,000,000	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														$ (2,096,000,000)	(1,845,000,000)	(1,621,000,000)
Recognized TCCA fees that had not been remitted to Treasury as of period end					$ 544,000,000				487,000,000					544,000,000	487,000,000
US Treasury [Member] | Other Expense [Member]
Related Parties [Line Items]
Affordable Housing Program Assessments														84,000,000	137,000,000	111,000,000
US Treasury [Member] | U.S. Treasury Securities [Member]
Related Parties [Line Items]
Trading, at fair value					29,200,000,000				32,300,000,000					29,200,000,000	32,300,000,000
Interest Income recognized on Treasury Securities														345,000,000	157,000,000	35,000,000
Accrued interest receivable					77,000,000				39,000,000					77,000,000	39,000,000
US Treasury [Member] | Scenario, Forecast [Member]
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement																	$ 119,800,000,000
Aggregate liquidation preference of senior preferred stock																	123,800,000,000
Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement																	$ 113,900,000,000
Freddie Mac [Member] | Freddie Mac [Member]
Related Parties [Line Items]
Fair value of mortgage-related securities					613,000,000				1,400,000,000					613,000,000	1,400,000,000
Accrued interest receivable					$ 2,000,000				$ 5,000,000					2,000,000	5,000,000
Investment income, interest														38,000,000	112,000,000	226,000,000
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees/expense														112,000,000	114,000,000	112,000,000
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire Equity Method Investments														$ 102,000,000	$ 118,000,000	$ 66,000,000