Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined benefit obligation, period increase		$ 2,130.0	$ 2,890.0
Curtailment gain	$ 28.0
Expense under the plans		$ 164.3	145.2	$ 132.6
Percentage of global investments in plan assets		80.00%
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain		$ 0.0	(2.2)	$ (1.3)
Total accumulated benefit obligation for our defined benefit pension plans		17,030.0	$ 15,170.0
Expected future employer contributions, next fiscal year		40.0
Expected future employer discretionary contributions, next fiscal year		$ 10.0
Marketable equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation		65.00%
Developed markets
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation		35.00%