Retirement Benefits - Obligations and Funded Status (Details) - USD ($) $ in Millions		12 Months Ended
	Oct. 08, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year		$ 1,066.1	$ 1,191.8
Service cost		9.9	10.5	$ 11.3
Interest cost		44.5	43.7	50.3
Participant contributions		0.1	0.3
Plan amendments		(0.6)	0.0
Plan combinations		1.4	0.7
Curtailment		(0.8)	0.0
Settlements		(54.5)	0.0
Benefits paid		(67.3)	(66.1)
Divestitures(a)		0.0	(3.9)
Actuarial (gains) losses		136.7	(88.7)
Foreign currency exchange effects		9.7	(22.2)
Benefit obligation at end of year		1,145.2	1,066.1	1,191.8
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		867.2	980.1
Return on assets – actual		143.3	(51.2)
Participant contributions		0.1	0.3
Employer contributions		14.6	17.4
Plan combinations		1.4	0.7
Settlements		(53.9)	0.0
Benefits paid		(67.3)	(66.1)
Foreign currency exchange effects		9.0	(14.0)
Fair value of plan assets at end of year		914.4	867.2	980.1
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		(230.8)	(198.9)
Current liability, included in accrued liabilities		1.9	2.0
Noncurrent liability		228.9	196.9
Net pension liability		230.8	198.9
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses		(368.0)	(391.8)
Net actuarial gains (losses) arising during the year		(53.0)	(27.2)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)		45.2	46.4
Foreign currency exchange effects		(2.3)	4.6
End of year - net gains and losses		(378.1)	(368.0)	(391.8)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit		(1.2)	(8.3)
Prior service credit (cost) from plan amendments during the year		0.6	0.0
Reclassification adjustment for amortization of prior service cost included in net income (loss)		0.1	7.1
Foreign currency exchange effects		0.0	0.0
End of year - net prior service (cost) credit		(0.5)	(1.2)	(8.3)
Retirement benefits other than pension
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year		555.6	589.3
Service cost		0.2	0.2	0.1
Interest cost		21.1	20.3	21.6
Plan amendments		(0.3)	0.0
Acquisition		0.9	0.2
Curtailment		(0.2)	0.0
Benefits paid		(37.8)	(36.8)
Actuarial (gains) losses		(2.6)	(16.5)
Foreign currency exchange effects		(0.2)	(1.1)
Benefit obligation at end of year		536.7	555.6	589.3
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		181.7	219.2
Return on assets – actual		25.9	(7.6)
Employer contributions		8.5	8.2
Net transfers to (from) plan assets		(0.4)	(1.3)
Benefits paid		(37.8)	(36.8)
Fair value of plan assets at end of year		177.9	181.7	219.2
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		(358.8)	(373.9)
Current liability, included in accrued liabilities		11.0	7.8
Noncurrent liability		347.8	366.1
Net pension liability		358.8	373.9
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses		(333.8)	(352.8)
Net actuarial gains (losses) arising during the year		15.2	(7.8)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)		21.2	26.1
Foreign currency exchange effects		0.1	0.7
End of year - net gains and losses		(297.3)	(333.8)	(352.8)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit		34.2	38.0
Prior service credit (cost) from plan amendments during the year		0.3	0.0
Reclassification adjustment for amortization of prior service cost included in net income (loss)		(5.1)	(3.5)
Foreign currency exchange effects		0.0	(0.3)
End of year - net prior service (cost) credit		29.4	34.2	38.0
U.S. Plans
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year		801.9	890.3
Service cost		0.0	0.0	0.0
Interest cost		34.1	31.9	35.1
Participant contributions		0.0	0.0
Plan amendments		0.0	0.0
Plan combinations		0.0	0.0
Settlements		(53.6)	0.0
Benefits paid		(49.1)	(49.3)
Actuarial (gains) losses		93.5	(71.0)
Foreign currency exchange effects		0.0	0.0
Benefit obligation at end of year		826.8	801.9	890.3
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		686.6	777.2
Return on assets – actual		114.1	(42.2)
Participant contributions		0.0	0.0
Employer contributions		0.7	0.9
Plan combinations		0.0	0.0
Settlements		(53.0)	0.0
Benefits paid		(49.1)	(49.3)
Foreign currency exchange effects		0.0	0.0
Fair value of plan assets at end of year		699.3	686.6	777.2
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		(127.5)	(115.3)
Current liability, included in accrued liabilities		0.6	1.2
Noncurrent liability		126.9	114.1
Net pension liability		127.5	115.3
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses		(306.0)	(308.9)
Net actuarial gains (losses) arising during the year		(29.5)	(24.8)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)		38.9	27.7
Foreign currency exchange effects		0.0	0.0
End of year - net gains and losses		(296.6)	(306.0)	(308.9)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit		0.0	0.0
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)		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
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		63.0
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		(96.0)
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		5.0
U.S. Plans | Total
Changes in the benefit obligation [Roll Forward]
Settlements	$ (54.0)
Non-U.S. Plans
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year		264.2	301.5
Service cost		9.9	10.5	11.3
Interest cost		10.4	11.8	15.2
Participant contributions		0.1	0.3
Plan amendments		(0.6)	0.0
Plan combinations		1.4	0.7
Curtailment		(0.8)
Settlements		(0.9)	0.0
Benefits paid		(18.2)	(16.8)
Divestitures(a)		0.0	(3.9)
Actuarial (gains) losses		43.2	(17.7)
Foreign currency exchange effects		9.7	(22.2)
Benefit obligation at end of year		318.4	264.2	301.5
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		180.6	202.9
Return on assets – actual		29.2	(9.0)
Participant contributions		0.1	0.3
Employer contributions		13.9	16.5
Plan combinations		1.4	0.7
Settlements		(0.9)	0.0
Benefits paid		(18.2)	(16.8)
Foreign currency exchange effects		9.0	(14.0)
Fair value of plan assets at end of year		215.1	180.6	202.9
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		(103.3)	(83.6)
Current liability, included in accrued liabilities		1.3	0.8
Noncurrent liability		102.0	82.8
Net pension liability		103.3	83.6
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses		(62.0)	(82.9)
Net actuarial gains (losses) arising during the year		(23.5)	(2.4)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)		6.3	18.7
Foreign currency exchange effects		(2.3)	4.6
End of year - net gains and losses		(81.5)	(62.0)	(82.9)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit		(1.2)	(8.3)
Prior service credit (cost) from plan amendments during the year		0.6	0.0
Reclassification adjustment for amortization of prior service cost included in net income (loss)		0.1	7.1
Foreign currency exchange effects		0.0	0.0
End of year - net prior service (cost) credit		(0.5)	(1.2)	(8.3)
Non-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		19.0
Non-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		37.0
UMWA Plans
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year		479.1	513.5
Service cost		0.0	0.0	0.0
Interest cost		17.3	17.1	18.4
Plan amendments		0.0	0.0
Curtailment		0.0	0.0
Benefits paid		(29.3)	(28.6)
Actuarial (gains) losses		(42.5)	(22.9)
Foreign currency exchange effects		0.0	0.0
Benefit obligation at end of year		424.6	479.1	513.5
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		181.7	219.2
Return on assets – actual		25.9	(7.6)
Net transfers to (from) plan assets		(0.4)	(1.3)
Benefits paid		(29.3)	(28.6)
Fair value of plan assets at end of year		177.9	181.7	219.2
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		(246.7)	(297.4)
Current liability, included in accrued liabilities		0.0	0.0
Noncurrent liability		246.7	297.4
Net pension liability		246.7	297.4
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses		(290.9)	(309.8)
Net actuarial gains (losses) arising during the year		55.1
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)		16.6	20.3
Foreign currency exchange effects		0.0	0.0
End of year - net gains and losses		(219.2)	(290.9)	(309.8)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit		32.7	37.3
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)		(4.7)	(4.6)
Foreign currency exchange effects		0.0	0.0
End of year - net prior service (cost) credit		28.0	32.7	37.3
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		13.0
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		(50.0)
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		6.0
UMWA 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		4.0
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		53.0
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		29.0
Black Lung and Other Plans
Changes in the benefit obligation [Roll Forward]
Benefit obligation at beginning of year		76.5	75.8
Service cost		0.2	0.2	0.1
Interest cost		3.8	3.2	3.2
Plan amendments		(0.3)	0.0
Acquisition		0.9	0.2
Curtailment		(0.2)	0.0
Benefits paid		(8.5)	(8.2)
Actuarial (gains) losses		39.9	6.4
Foreign currency exchange effects		(0.2)	(1.1)
Benefit obligation at end of year		112.1	76.5	75.8
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		8.5	8.2
Benefits paid		(8.5)	(8.2)
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		(112.1)	(76.5)
Current liability, included in accrued liabilities		11.0	7.8
Noncurrent liability		101.1	68.7
Net pension liability		112.1	76.5
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Beginning of year - net gains and losses		(42.9)	(43.0)
Net actuarial gains (losses) arising during the year		(39.9)
Reclassification adjustment for amortization of prior actuarial losses included in net income (loss)		4.6	5.8
Foreign currency exchange effects		0.1	0.7
End of year - net gains and losses		(78.1)	(42.9)	(43.0)
Benefit plan prior service cost recognized in accumulated other comprehensive income (loss):
Beginning of year - net prior service (cost) credit		1.5	0.7
Prior service credit (cost) from plan amendments during the year		0.3	0.0
Reclassification adjustment for amortization of prior service cost included in net income (loss)		(0.4)	1.1
Foreign currency exchange effects		0.0	(0.3)
End of year - net prior service (cost) credit		1.4	1.5	$ 0.7
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		(5.0)
Black Lung and Other 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		3.0
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		(8.0)
Black Lung and Other 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		$ (27.0)
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)
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
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 | UMWA Plans
Benefit plan net actuarial losses recognized in accumulated other comprehensive income (loss):
Net actuarial gains (losses) arising during the year			(1.4)
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)
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
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 | 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)
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)