Retirement Benefits (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 89.1	$ 92.0
Interest cost	100.5	84.3
Expected return on plan assets	(239.5)	(238.0)
Amortization of prior service cost	0.7	1.1
Recognized actuarial loss	87.0	121.8
Net periodic benefit cost	37.8	61.2
Retiree Health Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	11.2	11.7
Interest cost	9.4	8.1
Expected return on plan assets	(37.9)	(36.6)
Amortization of prior service cost	(13.7)	(14.9)
Recognized actuarial loss	0.2	0.8
Net periodic benefit cost	$ (30.8)	$ (30.9)