Benefit Plans and Other Postretirement Benefits, Defined Contribution Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Administrative Expense	$ 2	$ 2	$ 2
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for year-end valuation (as a percent)	2.65%	3.47%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65	5.50%	6.00%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65	5.00%	5.10%
Ultimate health care trend assumption rate (as a percent)	4.50%	4.50%
Period until ultimate trend rate is reached (in years)	5	3
Net benefit cost recognized for financial reporting	$ 1	$ 1	1
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for year-end valuation (as a percent)	2.71%	3.49%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	3.75%	3.75%
Net benefit cost recognized for financial reporting	$ 13	$ 6	$ 11
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan | Parent Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Net benefit cost recognized for financial reporting	$ 6	$ 4