Employee Benefit Plans and Equity Compensation Plan (Tables)

12 Months Ended

Dec. 31, 2020

Compensation And Retirement Disclosure [Abstract]

Schedule of Changes in Projected Benefit Obligations

The measurement date used to determine pension and other postretirement benefit obligations is December 31. Data related to the changes in the projected benefit obligation for pension benefits and the accumulated benefit obligation for other postretirement benefits are presented below.

	Pension Benefits						Other Postretirement Benefits
(millions)	2020			2019			2020			2019
Benefit obligation, January 1	$	727		$	732		$	214		$	187
Service cost		12			15			3			3
Interest cost		24			28			8			9
Plan participants’ contributions		—			—			2			1
Actuarial (gain) loss		41			47			(31	)		22
Benefits paid		(22	)		(21	)		(13	)		(13	)
Settlements		(40	)		(80	)		—			—
Curtailment		—			6			—			3
Amounts funded to parent		—			—			1			2
Benefit obligation, December 31	$	742		$	727		$	184		$	214

Schedule of Assumptions Used to Determine Benefit Obligations

Significant assumptions used to determine the above benefit obligations are as follows:

	Pension Benefits						Other Postretirement Benefits
	2020			2019			2020			2019
Annual discount rate used to determine benefit obligation		2.73	%		3.47	%		2.80	%		3.52	%
Assumed annual rate of future salary increases for projected    benefit obligation		4.52	%		3.00	%	N/A			N/A
Crediting interest rate for cash balance plans		1.93	%		2.67	%	N/A			N/A

Schedule of Net Funded Status

	Pension Benefits					Other Postretirement Benefits
At December 31,	2020		2019			2020			2019
(millions)
Fair value of plan assets	$	747	$	725		$	—		$	—
Benefit obligation		742		727			184			214
Funded status	$	5	$	(2	)	$	(184	)	$	(214	)

Schedule of Amounts Recognized in Balance Sheet

Amounts recognized on the consolidated balance sheets were as follows:

	Pension Benefits					Other Postretirement Benefits
At December 31,	2020		2019			2020			2019
(millions)
Noncurrent assets	$	5	$	—		$	—		$	—
Current liability		—		—			(11	)		(13	)
Noncurrent liability		—		(2	)		(173	)		(201	)

Schedule of Amounts Recognized in Accumulated Other Comprehensive Loss

Amounts recognized in accumulated other comprehensive loss were as follows:

	Pension Benefits				Other Postretirement Benefits
At December 31,	2020		2019		2020		2019
(millions)
Net actuarial loss	$	4	$	2	$	—	$	2

Schedule of Amounts Recognized in Regulatory Assets

Amounts recognized in regulatory assets were as follows:

	Pension Benefits				Other Postretirement Benefits
At December 31,	2020		2019		2020		2019
(millions)
Net actuarial loss	$	114	$	125	$	1	$	29

Schedule of Changes in Fair Value of Plan Assets

Changes in Fair Value of Plan Assets

Pension Benefits
(millions)	2020			2019
Fair value of plan assets, January 1	$	725		$	677
Actual return (loss) on plan assets		84			149
Benefits paid		(22	)		(21	)
Settlements		(40	)		(80	)
Fair value of plan assets, December 31	$	747		$	725

Schedule of Allocation of Plan Assets

The pension plan asset allocation at December 31, 2020 and 2019 and the target allocation for 2021 are as follows:

	Percentage of Plan Assets
	Target Allocation	December 31,
Asset Category	2021	2020			2019
U.S. equities	25 - 40%		34	%		40	%
Non-U.S. equities	10 - 20%		18	%		19	%
Fixed income	45- 65%		47	%		32	%
Cash and cash equivalents	2-10%		1	%		1	%
Company stock	0%		0	%		5	%
Real estate	0%		0	%		3	%

Schedule of Fair Value Measurements By Category

At December 31, 2020 and 2019, fair value measurements, and the level within the fair value hierarchy in which the measurements fall, were as follows:

At December 31,	2020		2019
(millions)
Investments with fair value measure at Level 1:
Cash and cash equivalents	$	10	$	3
Investments with fair value measure at Level 2:
Mutual funds		—		152
Corporate debt instruments		315		233
Government and other debt instruments		35		26
Total assets in the fair value hierarchy		360		414
Investments at net asset value:
Common collective trust		387		311
Total investments	$	747	$	725

Schedule of Expected Benefit Payments

Expected Benefit Payments

(millions)	Pension Benefits		Other Postretirement Benefits
2021	$	39	$	11
2022		45		11
2023		43		11
2024		45		11
2025		44		11
2026 - 2030		201		55

Components of Net Periodic Benefit Cost

Components of Net Periodic Benefit Cost

	Pension Benefits									Other Postretirement Benefits
Year Ended December 31,	2020			2019			2018			2020		2019		2018
(millions)
Service cost	$	12		$	15		$	17		$	3	$	3	$	4
Interest cost		24			28			29			8		9		8
Expected return on assets		(45	)		(40	)		(48	)		—		—		—
Prior service cost amortization		—			—			—			—		—		—
Amortization of actuarial losses		6			11			11			—		—		—
Settlement loss		7			16			—			—		—		—
Curtailment		—			6			—			—		3		—
Net periodic benefit cost	$	4		$	36		$	9		$	11	$	15	$	12

Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss)

Other changes in plan assets and benefit obligations recognized in other comprehensive income (net of tax) were as follows:

	Pension Benefits							Other Postretirement Benefits
Year Ended December 31,	2020		2019			2018		2020			2019		2018
(millions)
Current year actuarial (gain) loss	$	2	$	(1	)	$	1	$	(2	)	$	1	$	(1	)

Schedule of Defined Benefit Plan Amounts Recognized in Regulatory Assets

Other changes in plan assets and benefit obligations recognized in regulatory assets were as follows:

	Pension Benefits									Other Postretirement Benefits
Year Ended December 31,	2020			2019			2018			2020			2019		2018
(millions)
Current year actuarial (gain) loss	$	1		$	(51	)	$	41		$	(27	)	$	20	$	(26	)
Amortization of actuarial losses		(6	)		(11	)		(10	)		(1	)		—		(1	)
Settlement loss		(6	)		(16	)		—			—			—		—
Total recognized in regulatory assets	$	(11	)	$	(78	)	$	31		$	(28	)	$	20	$	(27	)

Schedule of Assumptions Used in Determining Net Periodic Benefit Cost

Significant assumptions used in determining net periodic benefit cost:

	Pension Benefits			Other Postretirement Benefits
Year Ended December 31,	2020	2019	2018	2020	2019	2018
Discount rate	3.47%	3.57/4.38%	3.71%	2.80%	4.08/4.41%	3.74%
Expected return on plan assets	7.00%	7.00%	7.00%	n/a	n/a	n/a
Rate of compensation increase	3.00%	3.00%	3.00%	n/a	n/a	n/a
Crediting interest rate for cash balance plans	2.67%	2.77/3.58%	4.00%	n/a	n/a	n/a
Health care cost trend rate				6.25%	6.60%	7.00%
Ultimate health care cost trend rate				5.00%	5.00%	5.00%
Year achieved				2025-2026	2023	2023