Retirement Benefits and Trusteed Assets (Pension Plan - Fair Value Measurements) (Details) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 3,960	$ 3,897	$ 5,507
Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	100	77
Equity Securities, Domestic
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	550	483
Equity Securities, International
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	364	481
Fixed Income Securities, Governmental
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	609	583
Fixed Income Securities, Corporate
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,323	1,203
Hedge Funds and Similar Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	282	321
Private Equity and Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	732	749
Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	790	734
Level 1 | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	100	77
Level 1 | Equity Securities, Domestic
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 1 | Equity Securities, International
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	55	65
Level 1 | Fixed Income Securities, Governmental
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	531	506
Level 1 | Fixed Income Securities, Corporate
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 1 | Hedge Funds and Similar Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	104	86
Level 1 | Private Equity and Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,469	1,330
Level 2 | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2 | Equity Securities, Domestic
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2 | Equity Securities, International
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2 | Fixed Income Securities, Governmental
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	78	77
Level 2 | Fixed Income Securities, Corporate
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,323	1,203
Level 2 | Hedge Funds and Similar Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	68	50
Level 2 | Private Equity and Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,701	1,833
Other | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Other | Equity Securities, Domestic
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	550	483
Other | Equity Securities, International
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	309	416
Other | Fixed Income Securities, Governmental
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Other | Fixed Income Securities, Corporate
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Other | Hedge Funds and Similar Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	110	185
Other | Private Equity and Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 732	$ 749