Retirement Benefits (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 88.2	$ 93.3	$ 177.3	$ 185.3
Interest cost	99.6	84.8	200.1	169.1
Expected return on plan assets	(237.0)	(237.2)	(476.5)	(475.2)
Amortization of prior service cost	0.6	1.1	1.3	2.2
Recognized actuarial loss	84.5	122.6	171.5	244.4
Net periodic benefit cost	35.9	64.6	73.7	125.8
Retiree Health Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	12.1	12.9	23.3	24.6
Interest cost	9.6	8.2	19.0	16.3
Expected return on plan assets	(38.2)	(36.5)	(76.1)	(73.1)
Amortization of prior service cost	(13.7)	(14.9)	(27.4)	(29.8)
Recognized actuarial loss	0.3	0.8	0.5	1.6
Net periodic benefit cost	$ (29.9)	$ (29.5)	$ (60.7)	$ (60.4)