In April 2012, FHFA issued Advisory Bulletin AB 2012-02, “Framework for Adversely Classifying Loans, Other Real Estate Owned, and Other Assets and Listing Assets for Special Mention” (the “Advisory Bulletin”), which prescribes, among other things, classification of loans by risk category and provides guidance on when a loan should be charged off. The provisions of the Advisory Bulletin led us to re-evaluate our estimate of when a loan is deemed uncollectible. For the vast majority of our delinquent single-family loans, we will continue to charge-off the loan at the date of foreclosure or other liquidation event (such as a deed-in-lieu of foreclosure or a short sale). For a relatively small subset of delinquent loans deemed to be uncollectible prior to foreclosure based upon our historical data, we charge off the portion of the loan (including preforeclosure taxes and insurance receivables that pertain to such loans) deemed to be uncollectible prior to the date of foreclosure or other liquidation event, which given our current credit analytics and historical data, is when the loans are excessively delinquent and the outstanding loan balance exceeds the fair value of the underlying property. This change in estimate resulted in the charge-offs of preforeclosure taxes and insurance receivables.

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Balance Type:	debit
Period Type:	instant

Summary of Significant Accounting Policies Use of Estimates (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2015
Change in Accounting Estimate [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%	35.00%	35.00%
Fair value of guaranty obligation		$ 276	$ 446
Change in Accounting Method Accounted for as Change in Estimate [Member]
Change in Accounting Estimate [Line Items]
Advisory Bulletin impact for HFI loans					$ (1,800)
Advisory Bulletin impact for preforeclosure property taxes and insurance receivable					$ (724)