Allowance for Credit Losses (Roll-forward of Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance, beginning of period			$ 1
Balance, end of period	$ 1		1
Residential Portfolio Segment [Member] | Conventional Mortgage Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance, beginning of period	1	$ 1	1	$ 1
Provision for credit losses	0	0	0	0
Balance, end of period	$ 1	$ 1	$ 1	$ 1