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Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended
	Dec. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer		$ 15	$ 18
Estimated future employer contributions in current fiscal year		91
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		56	56
UNITED KINGDOM
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		$ 69	$ 56
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%
Actual asset allocation percentage of equity (as a percent)		49.00%
Equity Funds \| UNITED KINGDOM
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		7.00%
Actual asset allocation percentage of equity (as a percent)		8.00%
Fixed Income Funds \| United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		50.00%
Actual asset allocation percentage of equity (as a percent)		51.00%
Fixed Income Funds \| UNITED KINGDOM
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		93.00%
Actual asset allocation percentage of equity (as a percent)		92.00%