Retirement Benefits - Obligations and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year	$ 1,191.8	$ 1,113.2
Service cost	10.5	11.3	$ 10.5
Interest cost	43.7	50.3	48.6
Participant contributions	0.3	0.4
Plan combinations	0.7	0.6
Acquisition	0.0	2.5
Settlements	0.0	(1.0)
Benefits paid	(66.1)	(65.7)
Divestitures(a)	(3.9)	0.0
Actuarial (gains) losses	(88.7)	65.8
Foreign currency exchange effects	(22.2)	14.4
Benefit obligation at end of year	1,066.1	1,191.8	1,113.2
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	980.1	901.9
Return on assets – actual	(51.2)	113.2
Participant contributions	0.3	0.4
Employer contributions	17.4	17.5
Settlements	0.0	(1.0)
Benefits paid	(66.1)	(65.7)
Foreign currency exchange effects	(14.0)	13.2
Fair value of plan assets at end of year	867.2	980.1	901.9
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status	(198.9)	(211.7)
Current liability, included in accrued liabilities	2.0	2.9
Noncurrent liability	196.9	208.8
Net pension liability	198.9	211.7
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses	(391.8)	(403.8)
Net actuarial gains (losses) arising during the year	(27.2)	(15.8)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)	46.4	33.9
Foreign currency exchange effects	4.6	(6.1)
End of year - net gains and losses	(368.0)	(391.8)	(403.8)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit	(8.3)	(9.2)
Reclassification adjustment for amortization of prior service cost included in net income (loss)	7.1	1.1
Foreign currency exchange effects	0.0	(0.2)
End of year - net prior service (cost) credit	(1.2)	(8.3)	(9.2)
Retirement benefits other than pension
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year	589.3	510.3
Service cost	0.2	0.1	0.0
Interest cost	20.3	21.6	21.6
Plan amendments	0.0	(1.1)
Acquisition	0.2
Curtailment	0.0	(2.4)
Benefits paid	(36.8)	(40.9)
Actuarial (gains) losses	(16.5)	101.7
Foreign currency exchange effects	(1.1)	0.0
Benefit obligation at end of year	555.6	589.3	510.3
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	219.2	217.6
Return on assets – actual	(7.6)	34.6
Employer contributions	6.9	7.9
Benefits paid	(36.8)	(40.9)
Fair value of plan assets at end of year	181.7	219.2	217.6
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status	(373.9)	(370.1)
Current liability, included in accrued liabilities	7.8	7.3
Noncurrent liability	366.1	362.8
Net pension liability	373.9	370.1
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses	(352.8)	(295.2)
Net actuarial gains (losses) arising during the year	(7.8)	(81.2)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)	26.1	23.6
Foreign currency exchange effects	0.7	0.0
End of year - net gains and losses	(333.8)	(352.8)	(295.2)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit	38.0	39.8
Prior service credit (cost) from plan amendments during the year	0.0	1.1
Reclassification adjustment for amortization of prior service cost included in net income (loss)	(3.5)	(3.0)
Foreign currency exchange effects	(0.3)	0.1
End of year - net prior service (cost) credit	34.2	38.0	39.8
U.S. Plans
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year	890.3	845.9
Service cost	0.0	0.0	0.0
Interest cost	31.9	35.1	37.1
Participant contributions	0.0	0.0
Plan combinations	0.0	0.0
Acquisition	0.0	0.0
Settlements	0.0	0.0
Benefits paid	(49.3)	(49.1)
Actuarial (gains) losses	(71.0)	58.4
Foreign currency exchange effects	0.0	0.0
Benefit obligation at end of year	801.9	890.3	845.9
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	777.2	728.5
Return on assets – actual	(42.2)	97.1
Participant contributions	0.0	0.0
Employer contributions	0.9	0.7
Settlements	0.0	0.0
Benefits paid	(49.3)	(49.1)
Foreign currency exchange effects	0.0	0.0
Fair value of plan assets at end of year	686.6	777.2	728.5
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status	(115.3)	(113.1)
Current liability, included in accrued liabilities	1.2	0.7
Noncurrent liability	114.1	112.4
Net pension liability	115.3	113.1
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses	(308.9)	(320.9)
Net actuarial gains (losses) arising during the year	(24.8)	(14.6)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)	27.7	26.6
Foreign currency exchange effects	0.0	0.0
End of year - net gains and losses	(306.0)	(308.9)	(320.9)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit	0.0	0.0
Reclassification adjustment for amortization of prior service cost included in net income (loss)	0.0	0.0
Foreign currency exchange effects	0.0	0.0
End of year - net prior service (cost) credit	0.0	0.0	0.0
Non-U.S. Plans
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year	301.5	267.3
Service cost	10.5	11.3	10.5
Interest cost	11.8	15.2	11.5
Participant contributions	0.3	0.4
Plan combinations	0.7	0.6
Acquisition	0.0	2.5
Settlements	0.0	(1.0)
Benefits paid	(16.8)	(16.6)
Divestitures(a)	(3.9)
Actuarial (gains) losses	(17.7)	7.4
Foreign currency exchange effects	(22.2)	14.4
Benefit obligation at end of year	264.2	301.5	267.3
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	202.9	173.4
Return on assets – actual	(9.0)	16.1
Participant contributions	0.3	0.4
Employer contributions	16.5	16.8
Settlements	0.0	(1.0)
Benefits paid	(16.8)	(16.6)
Foreign currency exchange effects	(14.0)	13.2
Fair value of plan assets at end of year	180.6	202.9	173.4
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status	(83.6)	(98.6)
Current liability, included in accrued liabilities	0.8	2.2
Noncurrent liability	82.8	96.4
Net pension liability	83.6	98.6
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses	(82.9)	(82.9)
Net actuarial gains (losses) arising during the year	(2.4)	(1.2)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)	18.7	7.3
Foreign currency exchange effects	4.6	(6.1)
End of year - net gains and losses	(62.0)	(82.9)	(82.9)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit	(8.3)	(9.2)
Reclassification adjustment for amortization of prior service cost included in net income (loss)	7.1	1.1
Foreign currency exchange effects	0.0	(0.2)
End of year - net prior service (cost) credit	(1.2)	(8.3)	(9.2)
UMWA Plans
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year	513.5	444.2
Service cost	0.0	0.0	0.0
Interest cost	17.1	18.4	18.9
Plan amendments	0.0	0.0
Curtailment	0.0	0.0
Benefits paid	(28.6)	(33.5)
Actuarial (gains) losses	(22.9)	84.4
Foreign currency exchange effects	0.0	0.0
Benefit obligation at end of year	479.1	513.5	444.2
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	219.2	217.6
Return on assets – actual	(7.6)	34.6
Employer contributions	(1.3)	0.5
Benefits paid	(28.6)	(33.5)
Fair value of plan assets at end of year	181.7	219.2	217.6
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status	(297.4)	(294.3)
Current liability, included in accrued liabilities	0.0	0.0
Noncurrent liability	297.4	294.3
Net pension liability	297.4	294.3
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses	(309.8)	(263.0)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)	20.3	19.5
Foreign currency exchange effects	0.0	0.0
End of year - net gains and losses	(290.9)	(309.8)	(263.0)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit	37.3	41.9
Prior service credit (cost) from plan amendments during the year	0.0	0.0
Reclassification adjustment for amortization of prior service cost included in net income (loss)	(4.6)	(4.6)
Foreign currency exchange effects	0.0	0.0
End of year - net prior service (cost) credit	32.7	37.3	41.9
Black Lung and Other Plans
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year	75.8	66.1
Service cost	0.2	0.1	0.0
Interest cost	3.2	3.2	2.7
Plan amendments	0.0	(1.1)
Acquisition	0.2
Curtailment	0.0	(2.4)
Benefits paid	(8.2)	(7.4)
Actuarial (gains) losses	6.4	17.3
Foreign currency exchange effects	(1.1)	0.0
Benefit obligation at end of year	76.5	75.8	66.1
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	0.0	0.0
Return on assets – actual	0.0	0.0
Employer contributions	8.2	7.4
Benefits paid	(8.2)	(7.4)
Fair value of plan assets at end of year	0.0	0.0	0.0
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status	(76.5)	(75.8)
Current liability, included in accrued liabilities	7.8	7.3
Noncurrent liability	68.7	68.5
Net pension liability	76.5	75.8
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses	(43.0)	(32.2)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)	5.8	4.1
Foreign currency exchange effects	0.7	0.0
End of year - net gains and losses	(42.9)	(43.0)	(32.2)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit	0.7	(2.1)
Prior service credit (cost) from plan amendments during the year	0.0	1.1
Reclassification adjustment for amortization of prior service cost included in net income (loss)	1.1	1.6
Foreign currency exchange effects	(0.3)	0.1
End of year - net prior service (cost) credit	1.5	0.7	$ (2.1)
ASU 2017-07 | U.S. Plans | Actuarial Gains (Losses) - Asset Return Different from Expected
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	(96.0)	44.0
ASU 2017-07 | U.S. Plans | Actuarial Gains (Losses) - Change in Discount Rate
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	65.0	(60.0)
ASU 2017-07 | U.S. Plans | Actuarial Gains (Losses) - Change of Mortality Tables
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	4.0
ASU 2017-07 | U.S. Plans | Actuarial Gains (Losses) - Change in Census Data
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year		3.0
ASU 2017-07 | UMWA Plans
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	(1.4)	(66.3)
ASU 2017-07 | UMWA Plans | Actuarial Gains (Losses) - Asset Return Different from Expected
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	(24.0)	18.0
ASU 2017-07 | UMWA Plans | Actuarial Gains (Losses) - Change in Discount Rate
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	33.0	(25.0)
ASU 2017-07 | UMWA Plans | Actuarial Gains (Losses) - Change of Mortality Tables
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	(32.0)
ASU 2017-07 | UMWA Plans | Actuarial Gains (Losses) - Claims Assumptions Updates
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	16.0
ASU 2017-07 | UMWA Plans | Actuarial Gains (Losses) - Change in Claims Experience
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year		(38.0)
ASU 2017-07 | UMWA Plans | Actuarial Gains (Losses) - Excise Tax Update
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year		(17.0)
ASU 2017-07 | Black Lung and Other Plans
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	(6.4)	$ (14.9)
ASU 2017-07 | Black Lung and Other Plans | Actuarial Gains (Losses) - Change in Discount Rate
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	4.0
ASU 2017-07 | Black Lung and Other Plans | Actuarial Gains (Losses) - Change in Census Data
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year	$ (9.0)