Allowance for Credit Losses (Mortgage Loan Portfolio by Impairment Methodology) (Details) - USD ($) $ in Millions	Jun. 30, 2019		Mar. 31, 2019	Dec. 31, 2018		Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Line Items]
Total allowance for credit losses	$ 1			$ 1
Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total recorded investment	330	[1]		362	[2]
Residential Portfolio Segment [Member] | Conventional Mortgage Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit losses, collectively evaluated for impairment	1			1
Total allowance for credit losses	1		$ 1	1		$ 1	$ 1	$ 1
Recorded investment, individually evaluated for impairment	9			9
Recorded investment, collectively evaluated for impairment	299			330
Total recorded investment	$ 308	[1]		$ 339	[2]

[1] The difference between the recorded investment and the carrying value of total mortgage loans of $1 relates to accrued interest.

[2] The difference between the recorded investment and the carrying value of total mortgage loans of $1 relates to accrued interest.