Retirement Benefits (Schedule of Benefit Obligations and Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in benefit obligation:
Curtailment	$ 159.0
Special termination benefit	354.7
Defined Benefit Pension Plans
Change in benefit obligation:
Benefit obligation at beginning of year	12,455.9	$ 11,719.2
Service cost	331.3	277.7	$ 315.7
Interest cost	413.4	420.8	476.8
Actuarial (gain) loss	1,580.5	806.5
Benefits paid	(486.3)	(454.5)
Plan amendments	0.0	0.0
Curtailment	90.4	0.0
Special termination benefit	317.2	0.0
Foreign currency exchange rate changes and other adjustments	396.0	(313.8)
Benefit obligation at end of year	15,098.4	12,455.9	11,719.2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	10,179.7	9,995.6
Actual return on plan assets	1,447.6	853.4
Employer contribution	414.3	110.2
Benefits paid	486.3	454.5
Foreign currency exchange rate changes and other adjustments	289.2	(325.0)
Fair value of plan assets at end of year	11,844.5	10,179.7	9,995.6
Funded status	(3,253.9)	(2,276.2)
Unrecognized net actuarial loss	5,645.5	4,915.7
Unrecognized prior service (benefit) cost	15.2	21.7
Net amount recognized	2,406.8	2,661.2
Retiree Health Benefit Plans
Change in benefit obligation:
Benefit obligation at beginning of year	1,494.6	1,467.4
Service cost	46.4	39.1	45.1
Interest cost	52.9	53.2	62.6
Actuarial (gain) loss	40.0	50.9
Benefits paid	(60.1)	(59.8)
Plan amendments	0.0	(35.8)
Curtailment	105.2	0.0
Special termination benefit	37.5	0.0
Foreign currency exchange rate changes and other adjustments	12.0	(20.4)
Benefit obligation at end of year	1,728.5	1,494.6	1,467.4
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	1,961.2	1,943.7
Actual return on plan assets	462.0	68.9
Employer contribution	9.1	8.4
Benefits paid	60.1	59.8
Foreign currency exchange rate changes and other adjustments	0.2	0.0
Fair value of plan assets at end of year	2,372.4	1,961.2	$ 1,943.7
Funded status	643.9	466.6
Unrecognized net actuarial loss	182.0	458.8
Unrecognized prior service (benefit) cost	(395.0)	(525.1)
Net amount recognized	$ 430.9	$ 400.3

Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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Amount of asset (liability), recognized in statement of financial position, for defined benefit pension and other postretirement plans.

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Amount of (increase) decrease in benefit obligation of defined benefit plan from event reducing expected years of future service of present employees or eliminating accrual of benefits for some or all future services of present employees.

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Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

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Amount of foreign currency translation gain (loss) which (increases) decreases benefit obligation of defined benefit plan.

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of increase (decrease) in benefit obligation of defined benefit plan from change in terms of existing plan or initiation of new plan.

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Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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Amount of foreign currency translation gain (loss) which increases (decreases) plan assets of defined benefit plan.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of increase in benefit obligation for benefits provided to employees payable from defined benefit plan or payable upon retirement.

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