Retirement Benefits (Narrative) (Details) $ in Millions, £ in Billions		3 Months Ended			9 Months Ended
	Dec. 31, 2024	Sep. 30, 2025 USD ($)	Sep. 30, 2025 GBP (£)	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, insurance policy investment for future benefit payments		$ 2,500	£ 1.9
Contributions by employer		21		$ 16	$ 56	$ 67
Estimated future employer contributions in current fiscal year		24			24
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		51		45	159	142
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		$ 43		$ 39	$ 141	$ 130
United Kingdom | Pension and Postretirement Benefit Plan, Defined Benefit | Geographic Concentration Risk
Defined Benefit Plan Disclosure [Line Items]
Concentration risk percentage (as a percent)	78.00%
Equity Funds | United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		50.00%			50.00%
Actual asset allocation percentage of equity (as a percent)		50.00%			50.00%
Equity Funds | United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		12.00%			12.00%
Actual asset allocation percentage of equity (as a percent)		9.00%			9.00%
Fixed Income Funds | United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		50.00%			50.00%
Actual asset allocation percentage of equity (as a percent)		50.00%			50.00%
Fixed Income Funds | United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		88.00%			88.00%
Actual asset allocation percentage of equity (as a percent)		91.00%			91.00%