Allowance for Credit Losses (Delinquent Mortgage Loans) (Details) - Conventional Mortgage Loan - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Total past due	[1]	$ 24	$ 26
Total current loans	[1]	3,310	3,058
Total mortgage loans	[1]	3,334	3,084
In process of foreclosure, included above	[1],[2]	0	3
Nonaccrual loans	[1]	$ 7	$ 9
Serious delinquencies as a percentage of total mortgage loans outstanding	[1],[3]	0.22%	0.31%
30 – 59 days delinquent
Financing Receivable, Allowance for Credit Loss [Line Items]
Total past due	[1]	$ 15	$ 15
60 – 89 days delinquent
Financing Receivable, Allowance for Credit Loss [Line Items]
Total past due	[1]	2	2
90 days or more delinquent
Financing Receivable, Allowance for Credit Loss [Line Items]
Total past due	[1]	$ 7	$ 9

[1] The recorded investment in a loan is the unpaid principal balance of the loan, adjusted for accrued interest, net deferred loan fees or costs, unamortized premiums or discounts, and direct write-downs. The recorded investment is not net of any valuation allowance.

[2] Includes loans for which the servicer has reported a decision to foreclose or to pursue a similar alternative, such as deed-in-lieu. Loans in process of foreclosure are included in past due or current loans depending on their delinquency status.

[3] Represents loans that are 90 days or more past due or in the process of foreclosure as a percentage of the recorded investment of total mortgage loans outstanding