Retirement Benefits (Schedule of Benefit Obligations and Plan Assets and Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Pension Plans
Change in benefit obligation:
Benefit obligation at beginning of year	$ 16,251.0	$ 13,427.1
Service cost	325.5	250.4	$ 292.7
Interest cost	425.8	486.0	458.5
Actuarial loss	1,563.1	2,631.7
Benefits paid	(587.2)	(584.2)
Curtailment (gain) loss	2.2	(16.8)
Foreign currency exchange rate changes and other adjustments	245.1	56.8
Benefit obligation at end of year	18,225.5	16,251.0	13,427.1
Change in plan assets:
Fair value of plan assets at beginning of year	12,858.0	10,932.6
Actual return on plan assets	1,802.4	2,012.0
Employer contribution	318.8	429.9
Benefits paid	(587.2)	(584.2)
Foreign currency exchange rate changes and other adjustments	187.0	67.7
Fair value of plan assets at end of year	14,579.0	12,858.0	10,932.6
Funded status	(3,646.5)	(3,393.0)
Unrecognized net actuarial (gain) loss	6,515.5	6,177.6
Unrecognized prior service (benefit) cost	15.4	17.4
Net amount recognized	2,884.4	2,802.0
Retiree Health Benefit Plans
Change in benefit obligation:
Benefit obligation at beginning of year	1,601.4	1,540.0
Service cost	40.8	36.3	41.5
Interest cost	43.7	58.0	57.3
Actuarial loss	142.1	54.3
Benefits paid	(75.1)	(87.3)
Curtailment (gain) loss	0.0	(0.5)
Foreign currency exchange rate changes and other adjustments	0.8	0.6
Benefit obligation at end of year	1,753.7	1,601.4	1,540.0
Change in plan assets:
Fair value of plan assets at beginning of year	2,768.2	2,398.1
Actual return on plan assets	539.0	444.1
Employer contribution	(5.1)	13.2
Benefits paid	(75.1)	(87.3)
Foreign currency exchange rate changes and other adjustments	0.0	0.1
Fair value of plan assets at end of year	3,227.0	2,768.2	$ 2,398.1
Funded status	1,473.3	1,166.8
Unrecognized net actuarial (gain) loss	(349.1)	(111.6)
Unrecognized prior service (benefit) cost	(177.6)	(236.4)
Net amount recognized	$ 946.6	$ 818.8