Retirement Benefits - Retirement Cost (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2014 USD ($) participant	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) participant	Dec. 31, 2013 USD ($)
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 0.0	$ 0.0	$ 0.0
Interest cost on projected benefit obligation		36.0	45.3	42.2
Return on assets – expected		(54.6)	(63.9)	(56.9)
Amortization of losses		31.2	28.2	45.1
Amortization of prior service cost		0.0	0.0	0.0
Settlement loss (a)	$ 56.1	0.0	56.1	0.1
Net periodic pension cost		12.6	$ 65.7	30.5
Number of participants | participant	4,300		4,300
U.S. Plans | Continuing operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost		12.6	$ 65.7	30.5
U.S. Plans | Discontinued operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost		0.0	0.0	0.0
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost		10.4	12.5	15.0
Interest cost on projected benefit obligation		11.2	18.4	19.1
Return on assets – expected		(9.5)	(14.4)	(12.9)
Amortization of losses		5.0	2.3	6.1
Amortization of prior service cost		0.9	1.0	0.8
Settlement loss (a)		5.7	6.3	2.6
Net periodic pension cost		23.7	26.1	30.7
Non-U.S. Plans | Continuing operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost		22.6	24.4	28.7
Non-U.S. Plans | Discontinued operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost		1.1	1.7	2.0
Total
Defined Benefit Plan Disclosure [Line Items]
Service cost		10.4	12.5	15.0
Interest cost on projected benefit obligation		47.2	63.7	61.3
Return on assets – expected		(64.1)	(78.3)	(69.8)
Amortization of losses		36.2	30.5	51.2
Amortization of prior service cost		0.9	1.0	0.8
Settlement loss (a)		5.7	62.4	2.7
Net periodic pension cost		36.3	91.8	61.2
Total | Continuing operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost		35.2	90.1	59.2
Total | Discontinued operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost		1.1	1.7	2.0
UMWA Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.0	0.0	0.0
Interest cost on projected benefit obligation		17.1	17.9	19.7
Return on assets – expected		(20.6)	(22.2)	(20.8)
Amortization of losses		15.5	12.3	19.6
Amortization of prior service cost		(4.6)	(4.6)	0.0
Curtailment (gain)		0.0	0.0	0.0
Net periodic pension cost		7.4	3.4	18.5
Black Lung and Other Plans, Medical
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.2	0.1	0.3
Interest cost on projected benefit obligation		2.8	2.3	1.9
Return on assets – expected		0.0	0.0	0.0
Amortization of losses		3.1	0.6	0.7
Amortization of prior service cost		1.8	1.7	1.7
Curtailment (gain)		(0.1)	0.0	0.0
Net periodic pension cost		7.8	4.7	4.6
Retirement benefits other than pension
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.2	0.1	0.3
Interest cost on projected benefit obligation		19.9	20.2	21.6
Return on assets – expected		(20.6)	(22.2)	(20.8)
Amortization of losses		18.6	12.9	20.3
Amortization of prior service cost		(2.8)	(2.9)	1.7
Curtailment (gain)		(0.1)	0.0	0.0
Net periodic pension cost		15.2	8.1	23.1
Post Retirement Benefits, Non US plans
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost		$ 1.1	$ 0.7	$ 0.7