Allowance for Credit Losses (By Impairment Methodology) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Total Allowance for Credit Losses		$ 0	$ 0
Conventional Mortgage Loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment, Allowance for credit losses		0	0
Collectively Evaluated for Impairment, Allowance for credit losses		0	0
Total Allowance for Credit Losses		0	0
Individually evaluated for impairment, Recorded investment		5	7
Collectively evaluated for impairment, Recorded investment		3,329	3,077
Total mortgage loans	[1]	$ 3,334	$ 3,084

[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.