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Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Dec. 31, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer		$ 27	$ 26	$ 51	$ 47
Estimated future employer contributions in current fiscal year		43		43
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		48	44	97	88
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		$ 39	$ 38	$ 91	$ 81
United Kingdom \| Defined Benefit Plan Assets Benchmark \| Geographic Concentration Risk
Defined Benefit Plan Disclosure [Line Items]
Concentration risk percentage	79.00%
Equity Funds \| United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		50.00%		50.00%
Actual asset allocation percentage of equity		51.00%		51.00%
Equity Funds \| United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		14.00%		14.00%
Actual asset allocation percentage of equity		14.00%		14.00%
Fixed Income Funds \| United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		50.00%		50.00%
Actual asset allocation percentage of equity		49.00%		49.00%
Fixed Income Funds \| United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		86.00%		86.00%
Actual asset allocation percentage of equity		86.00%		86.00%