Retirement Benefits (Schedule of Expected Benefit Payments, Contributions and Expense) (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, Pension Plan with Project Benefit Obligation in Excess of Plan Assets [Abstract]
Projected benefit obligation		$ 15,770.7	$ 14,039.7
Fair value of plan assets		11,824.4	10,483.4
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Fair value of plan assets		11,824.4	10,483.4
Components of net periodic (benefit) cost:
Curtailment (gain) loss	$ (28.0)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment and Tax [Abstract]
Total other comprehensive income (loss) during period		(157.1)	(970.0)	$ 544.0
Defined Benefit Pension Plans
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021		639.2
2022		635.3
2023		645.8
2024		673.1
2025		689.6
2026-2030		3,800.8
Defined Benefit Plan, Pension Plan with Project Benefit Obligation in Excess of Plan Assets [Abstract]
Fair value of plan assets		11,824.4	10,483.4
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Accumulated benefit obligation		14,682.3	13,063.7
Fair value of plan assets		11,824.4	10,483.4
Components of net periodic (benefit) cost:
Service cost		325.5	250.4	292.7
Interest cost		425.8	486.0	458.5
Expected return on plan assets		(901.5)	(839.6)	(842.1)
Amortization of prior service (benefit) cost		4.5	6.1	4.6
Recognized actuarial loss (gain)		396.3	284.9	332.5
Curtailment (gain) loss		0.0	2.2	1.3
Net periodic (benefit) cost		250.6	190.0	247.5
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment and Tax [Abstract]
Actuarial gain (loss) arising during period		(663.0)	(1,461.0)	182.8
Plan amendments during period		(2.2)	0.0	(17.6)
Curtailment gain (loss)		0.0	19.0	45.2
Amortization of prior service (benefit) cost included in net income		4.5	6.1	4.6
Amortization of net actuarial loss included in net income		396.3	284.9	332.5
Foreign currency exchange rate changes and other		(71.5)	(7.7)	47.1
Total other comprehensive income (loss) during period		(335.9)	(1,158.7)	594.6
Retiree Health Benefit Plans
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021		91.2
2022		91.2
2023		91.2
2024		94.9
2025		95.7
2026-2030		481.8
Defined Benefit Plan, Pension Plan with Project Benefit Obligation in Excess of Plan Assets [Abstract]
Fair value of plan assets		0.0	0.0
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Accumulated benefit obligation		223.8	214.4
Fair value of plan assets		0.0	0.0
Components of net periodic (benefit) cost:
Service cost		40.8	36.3	41.5
Interest cost		43.7	58.0	57.3
Expected return on plan assets		(158.1)	(144.3)	(177.9)
Amortization of prior service (benefit) cost		(59.5)	(62.9)	(79.5)
Recognized actuarial loss (gain)		(3.0)	1.9	6.1
Curtailment (gain) loss		0.0	0.0	(29.3)
Net periodic (benefit) cost		(136.1)	(111.0)	(181.8)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment and Tax [Abstract]
Actuarial gain (loss) arising during period		238.8	246.1	37.5
Plan amendments during period		0.0	0.0	14.1
Curtailment gain (loss)		0.0	0.0	(31.8)
Amortization of prior service (benefit) cost included in net income		(59.5)	(62.9)	(79.5)
Amortization of net actuarial loss included in net income		(3.0)	1.9	6.1
Foreign currency exchange rate changes and other		2.4	3.6	(0.1)
Total other comprehensive income (loss) during period		$ 178.7	$ 188.7	$ (53.7)