Retirement Benefits (Components of Net Periodic (Benefit) Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 74.9	$ 88.2	$ 145.3	$ 177.3
Interest cost	162.6	99.6	323.7	200.1
Expected return on plan assets	(264.2)	(237.0)	(527.5)	(476.5)
Amortization of prior service cost	0.6	0.6	1.2	1.3
Recognized actuarial (gain) loss	30.9	84.5	60.9	171.5
Net periodic cost	4.8	35.9	3.6	73.7
Retiree Health Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	8.2	12.1	15.9	23.3
Interest cost	15.3	9.6	30.7	19.0
Expected return on plan assets	(45.6)	(38.2)	(91.1)	(76.1)
Amortization of prior service cost	(13.2)	(13.7)	(26.4)	(27.4)
Recognized actuarial (gain) loss	(2.0)	0.3	(2.9)	0.5
Net periodic cost	$ (37.3)	$ (29.9)	$ (73.8)	$ (60.7)