Employee Retirement Plans and Incentive Compensation Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Maximum Annual Contributions per Employee, Percent	20.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Defined Contribution Plan, Cost	$ 2	$ 2	$ 2
Deferred Compensation Arrangement with Individual, Recorded Liability	49	41	$ 44
Defined Contribution Plan, Employer Discretionary Contribution Amount Liability	$ 17	$ 14
Cash Balance Plan
Defined Benefit Plan Disclosure [Line Items]
Cash Balance Plan Defined Benefit Accrual Percentage	6.00%
Cash Balance Plan Defined Benefit Interest	6.00%
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 6
Cash Balance Plan, Expected Future Employer Contributions, Next Twelve Months	$ 3
Non-Qualified Defined Benefit Plan - SERP
Defined Benefit Plan Disclosure [Line Items]
Non Qualified Defined Benetfit Interest	6.00%
Non-Qualified Defined Benefit Plans and Postretirement Health Benefit
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 2
Cash Balance Plan, Expected Future Employer Contributions, Next Twelve Months	$ 3
Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	60%
Real estate mutual funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	10%
Fixed income mutual funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	30%