Pension and Postretirement Health Care Benefits (Details) - USD ($)		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021		Dec. 31, 2020
Pension Benefits [Abstract]
annual interest crediting rates			$ 4.89		$ 2.03		$ 1.89
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan
Pension Benefits [Abstract]
Total benefit obligation			11,000,000		43,000,000
Net benefit cost recognized for financial reporting			17,000,000		4,000,000
Pension Plan [Member]
Pension Benefits [Abstract]
Total benefit obligation			2,871,000,000		3,718,000,000		3,964,000,000
Defined Benefit Plan, Plan Assets, Amount			2,685,000,000	[1]	3,670,000,000	[1]	3,599,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[1]		(882,000,000)		(1,175,000,000)
Net benefit cost recognized for financial reporting			$ 114,000,000		$ 121,000,000		$ 117,000,000
Expected average long-term rate of return on assets (as a percent)			6.49%		6.49%		6.87%
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			100.00%		100.00%
Pension Plan [Member] | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		$ 1,111,000,000		$ 1,524,000,000
Pension Plan [Member] | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		689,000,000		966,000,000
Pension Plan [Member] | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		3,000,000		5,000,000
Pension Plan [Member] | Equity Securities
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		47,000,000		67,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[1]		$ 0		$ 0
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			33.00%		33.00%
Pension Plan [Member] | Equity Securities | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		$ 47,000,000		$ 67,000,000
Pension Plan [Member] | Equity Securities | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		0		0
Pension Plan [Member] | Equity Securities | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		$ 0		$ 0
Pension Plan [Member] | Long-duration fixed income and interest rate swap securities
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			38.00%		37.00%
Pension Plan [Member] | Short-to-intermediate fixed income securities
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			9.00%		11.00%
Pension Plan [Member] | Alternative investments
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			18.00%		17.00%
Pension Plan [Member] | Cash
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		$ 129,000,000		$ 133,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[1]		$ 0		$ 0
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			2.00%		2.00%
Pension Plan [Member] | Cash | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		$ 129,000,000		$ 133,000,000
Pension Plan [Member] | Cash | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		0		0
Pension Plan [Member] | Cash | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		0		0
Pension Plan [Member] | Commingled Funds
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		1,817,000,000		2,467,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[1]		(882,000,000)		(1,143,000,000)
Pension Plan [Member] | Commingled Funds | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		935,000,000		1,324,000,000
Pension Plan [Member] | Commingled Funds | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		0		0
Pension Plan [Member] | Commingled Funds | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		0		0
Pension Plan [Member] | Debt Securities
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		685,000,000		964,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[1]		0		0
Pension Plan [Member] | Debt Securities | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		0		0
Pension Plan [Member] | Debt Securities | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		682,000,000		959,000,000
Pension Plan [Member] | Debt Securities | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		3,000,000		5,000,000
Pension Plan [Member] | Other
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		7,000,000		39,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[1]		0		32,000,000
Pension Plan [Member] | Other | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		0		0
Pension Plan [Member] | Other | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		7,000,000		7,000,000
Pension Plan [Member] | Other | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[1]		0		0
Other Postretirement Benefits Plan [Member]
Pension Benefits [Abstract]
Total benefit obligation			405,000,000		511,000,000		$ 574,000,000
Defined Benefit Plan, Plan Assets, Amount			364,000,000	[2]	442,000,000	[2]	452,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[2]		(63,000,000)		(77,000,000)
Net benefit cost recognized for financial reporting			$ (2,000,000)		$ (2,000,000)		$ (1,000,000)
Expected average long-term rate of return on assets (as a percent)			4.10%		4.10%		4.50%
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			100.00%		100.00%
Other Postretirement Benefits Plan [Member] | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		$ 85,000,000		$ 92,000,000
Other Postretirement Benefits Plan [Member] | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		215,000,000		272,000,000
Other Postretirement Benefits Plan [Member] | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		$ 1,000,000		$ 1,000,000
Other Postretirement Benefits Plan [Member] | Equity Securities
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			16.00%		15.00%
Other Postretirement Benefits Plan [Member] | Long-duration fixed income and interest rate swap securities
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			0.00%		0.00%
Other Postretirement Benefits Plan [Member] | Short-to-intermediate fixed income securities
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			71.00%		71.00%
Other Postretirement Benefits Plan [Member] | Alternative investments
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			12.00%		8.00%
Other Postretirement Benefits Plan [Member] | Cash
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		$ 31,000,000		$ 28,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[2]		$ 0		$ 0
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)			1.00%		6.00%
Other Postretirement Benefits Plan [Member] | Cash | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		$ 31,000,000		$ 28,000,000
Other Postretirement Benefits Plan [Member] | Cash | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		0		0
Other Postretirement Benefits Plan [Member] | Cash | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		0		0
Other Postretirement Benefits Plan [Member] | Commingled Funds
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		117,000,000		141,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[2]		(63,000,000)		(77,000,000)
Other Postretirement Benefits Plan [Member] | Commingled Funds | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		54,000,000		64,000,000
Other Postretirement Benefits Plan [Member] | Commingled Funds | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		0		0
Other Postretirement Benefits Plan [Member] | Commingled Funds | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		0		0
Other Postretirement Benefits Plan [Member] | Debt Securities
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		176,000,000		219,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[2]		0		0
Other Postretirement Benefits Plan [Member] | Debt Securities | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		0		0
Other Postretirement Benefits Plan [Member] | Debt Securities | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		175,000,000		218,000,000
Other Postretirement Benefits Plan [Member] | Debt Securities | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		1,000,000		1,000,000
Other Postretirement Benefits Plan [Member] | Other
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		(1,000,000)		2,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[2]		0		0
Other Postretirement Benefits Plan [Member] | Other | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		0		0
Other Postretirement Benefits Plan [Member] | Other | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		(1,000,000)		2,000,000
Other Postretirement Benefits Plan [Member] | Other | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		0		0
Other Postretirement Benefits Plan [Member] | Insurance contracts
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		41,000,000		52,000,000
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	[2]		0		0
Other Postretirement Benefits Plan [Member] | Insurance contracts | Level 1
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		0		0
Other Postretirement Benefits Plan [Member] | Insurance contracts | Level 2
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		41,000,000		52,000,000
Other Postretirement Benefits Plan [Member] | Insurance contracts | Level 3
Pension Benefits [Abstract]
Defined Benefit Plan, Plan Assets, Amount	[2]		$ 0		$ 0
Forecast | Pension Plan [Member]
Pension Benefits [Abstract]
Expected average long-term rate of return on assets for next fiscal year (as a percent)		6.93%

[1] See Note 10 for further information regarding fair value measurement inputs and methods.

[2] See Note 10 for further information on fair value measurement inputs and methods.