Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined benefit obligation, period decrease	$ 1,090.0	$ 4,750.0
Expense under the plans	$ 222.6	170.6	$ 167.3
Percentage of global investments in plan assets	85.00%
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for our defined benefit pension plans	$ 12,740.0	$ 12,010.0
Expected future employer contributions, next fiscal year	$ 40.0
Marketable equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation	75.00%
Developed markets
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation	25.00%