Benefit Plans and Other Postretirement Benefits, Pension Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Operating and maintenance expenses		$ 191,000,000	$ 201,000,000	$ 203,000,000
Target Pension Asset Allocations [Abstract]
annual interest crediting rates [Domain]		1.78	2.74	3.57
annual interest crediting rates [Domain]		1.78	2.74	3.57
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan
Pension Benefits [Abstract]
Total benefit obligation		1,000,000	1,000,000
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Operating and maintenance expenses			2,000,000
Pension Benefits [Abstract]
Total benefit obligation		154,000,000	144,000,000	140,000,000
Net benefit cost recognized for financial reporting		$ 13,000,000	$ 6,000,000	$ 11,000,000
Minimum number of years historical achieved weighted average annual returns are used to determine investment return assumptions (in years)		20 years
Expected average long-term rate of return on assets (as a percent)		7.10%	7.10%	7.10%
Target Pension Asset Allocations [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		100.00%	100.00%
Pension Plan [Member] | Domestic and international equity securities
Target Pension Asset Allocations [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		35.00%	37.00%
Pension Plan [Member] | Long-duration fixed income and interest rate swap securities
Target Pension Asset Allocations [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		35.00%	30.00%
Pension Plan [Member] | Short-to-intermediate fixed income securities
Target Pension Asset Allocations [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		13.00%	14.00%
Pension Plan [Member] | Alternative investments
Target Pension Asset Allocations [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		15.00%	17.00%
Pension Plan [Member] | Cash
Target Pension Asset Allocations [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		2.00%	2.00%
Forecast [Member] | Pension Plan [Member]
Pension Benefits [Abstract]
Expected average long-term rate of return on assets for next fiscal year (as a percent)	6.60%
Parent Company [Member] | Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan
Pension Benefits [Abstract]
Total benefit obligation		$ 43,000,000	$ 39,000,000
Net benefit cost recognized for financial reporting		$ 6,000,000	$ 4,000,000