Allowance for Credit Losses (Credit Quality Indicators) (Details) - Residential Portfolio Segment [Member] - USD ($) $ in Millions		Jun. 30, 2019		Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		$ 18		$ 19
Total current mortgage loans		312		343
Total recorded investment		330	[1]	362	[2]
In process of foreclosure	[3]	$ 1		$ 2
Seriously delinquent rate	[4]	1.43%		1.89%
Past due 90 days or more and still accruing interest	[5]	$ 0		$ 0
Loans on nonaccrual status	[6]	5		6
Accrued Interest on Mortgage Loans		1		1
Conventional Mortgage Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		15		17
Total current mortgage loans		293		322
Total recorded investment		308	[1]	339	[2]
In process of foreclosure	[3]	$ 1		$ 2
Seriously delinquent rate	[4]	1.49%		1.93%
Past due 90 days or more and still accruing interest	[5]	$ 0		$ 0
Loans on nonaccrual status	[6]	5		6
Government-guaranteed or insured mortgage loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		3		2
Total current mortgage loans		19		21
Total recorded investment		22	[1]	23	[2]
In process of foreclosure	[3]	$ 0		$ 0
Seriously delinquent rate	[4]	0.57%		1.23%
Past due 90 days or more and still accruing interest	[5]	$ 0		$ 0
Loans on nonaccrual status	[6]	0		0
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		11		10
Financial Asset, 30 to 59 Days Past Due [Member] | Conventional Mortgage Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		8		8
Financial Asset, 30 to 59 Days Past Due [Member] | Government-guaranteed or insured mortgage loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		3		2
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		2		3
Financial Asset, 60 to 89 Days Past Due [Member] | Conventional Mortgage Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		2		3
Financial Asset, 60 to 89 Days Past Due [Member] | Government-guaranteed or insured mortgage loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		0		0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		5		6
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Conventional Mortgage Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		5		6
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Government-guaranteed or insured mortgage loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total past due mortgage loans		$ 0		$ 0

[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.

[3] Includes mortgage loans where the decision of foreclosure or similar alternative, such as a pursuit of deed-in-lieu, has been reported. Mortgage loans in the process of foreclosure are included in past due categories depending on their delinquency status.

[4] Mortgage loans that are 90 days or more past due or in the process of foreclosure expressed as a percentage of the total mortgage loan portfolio segment.

[5] Mortgage loans insured or guaranteed by the Federal Housing Administration or the Department of Veterans Affairs.

[6] Represents mortgage loans with contractual principal or interest payments 90 days or more past due and not accruing interest.