Retirement Benefits (Schedule of Expected Benefit Payments, Contributions and Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets [Abstract]
Projected benefit obligation	$ 13,025.0	$ 10,597.0
Fair value of plan assets	9,664.3	8,291.2
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment and Tax [Abstract]
Total other comprehensive income (loss) during period	(576.6)	(512.8)	$ 572.9
Defined Benefit Pension Plans
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2018	(603.9)
2019	(601.4)
2020	(611.6)
2021	(621.4)
2022	(639.5)
2023-2027	(3,455.8)
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Accumulated benefit obligation	11,956.7	9,805.4
Fair value of plan assets	9,639.4	8,285.2
Components of net periodic (benefit) cost:
Service cost	331.3	277.7	315.7
Interest cost	413.4	420.8	476.8
Expected return on plan assets	(776.0)	(752.1)	(782.3)
Amortization of prior service (benefit) cost	5.7	11.8	10.4
Recognized actuarial loss	288.2	285.6	383.2
Curtailment	(93.5)	0.0	0.0
Special termination benefit	317.2	0.0	0.0
Net periodic (benefit) cost	673.3	243.8	403.8
Unrecognized net actuarial loss	(366.1)
Unrecognized prior service (benefit) cost	5.1
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment and Tax [Abstract]
Actuarial gain (loss) arising during period	(915.1)	(725.2)	120.4
Plan amendments during period	0.0	0.0	0.4
Curtailment	3.2	0.0	0.0
Amortization of prior service (benefit) cost included in net income	5.7	11.8	10.4
Amortization of net actuarial loss included in net income	288.2	285.6	383.2
Foreign currency exchange rate changes and other	(105.3)	75.6	58.8
Total other comprehensive income (loss) during period	(723.3)	(352.2)	573.2
Retiree Health Benefit Plans
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2018	(92.8)
2019	(94.8)
2020	(96.5)
2021	(98.7)
2022	(98.5)
2023-2027	(496.3)
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Accumulated benefit obligation	225.1	222.7
Fair value of plan assets	0.0	0.0
Components of net periodic (benefit) cost:
Service cost	46.4	39.1	45.1
Interest cost	52.9	53.2	62.6
Expected return on plan assets	(160.7)	(150.2)	(150.0)
Amortization of prior service (benefit) cost	(90.0)	(85.8)	(91.1)
Recognized actuarial loss	18.4	19.1	38.0
Curtailment	(65.5)	0.0	0.0
Special termination benefit	37.5	0.0	0.0
Net periodic (benefit) cost	(30.0)	(124.6)	(95.4)
Unrecognized net actuarial loss	(9.5)
Unrecognized prior service (benefit) cost	(81.3)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment and Tax [Abstract]
Actuarial gain (loss) arising during period	261.3	(132.2)	48.6
Plan amendments during period	0.0	35.8	0.0
Curtailment	(39.7)	0.0	0.0
Amortization of prior service (benefit) cost included in net income	(90.0)	(85.8)	(91.1)
Amortization of net actuarial loss included in net income	18.4	19.1	38.0
Foreign currency exchange rate changes and other	(3.3)	2.5	4.2
Total other comprehensive income (loss) during period	$ 146.7	$ (160.6)	$ (0.3)