Accumulated Other Comprehensive Income (Loss) - Reclassification from AOCI (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
	Apr. 01, 2017	Jun. 30, 2017	Apr. 01, 2017	Jun. 30, 2016	Jun. 30, 2016
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax benefit (provision)	$ 266.0	$ (4.7)	$ 263.8	$ 37.6	$ 97.4
Total after income taxes				(223.2)	(390.9)
Predecessor
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating costs and expenses	0.0		(963.7)	(996.2)	(1,916.4)
Selling and administrative expenses	0.0		(37.2)	(34.2)	(82.5)
Income tax benefit (provision)	266.0		263.8	37.6	97.4
Total after income taxes	$ (319.8)		(195.5)	(223.2)	(390.9)
Successor
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating costs and expenses		(934.8)
Selling and administrative expenses		(34.4)
Income tax benefit (provision)		(4.7)
Total after income taxes		$ 101.4
Reclassification out of Accumulated Other Comprehensive Income | Net actuarial loss associated with postretirement plans and workers' compensation obligations
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Insignificant items			2.7	2.9	5.8
Total before income taxes			(9.1)	(8.4)	(16.7)
Income tax benefit (provision)			3.3	3.1	6.2
Total after income taxes			(5.8)	(5.3)	(10.5)
Reclassification out of Accumulated Other Comprehensive Income | Prior service credit associated with postretirement plans
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before income taxes			2.2	2.7	5.3
Income tax benefit (provision)			(0.8)	(1.0)	(2.0)
Total after income taxes			1.4	1.7	3.3
Reclassification out of Accumulated Other Comprehensive Income | Cash flow hedges
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before income taxes			(27.7)	(62.5)	(141.4)
Income tax benefit (provision)			9.1	23.1	52.3
Total after income taxes			(18.6)	(39.4)	(89.1)
Reclassification out of Accumulated Other Comprehensive Income | Foreign currency cash flow hedge contracts | Cash flow hedges
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating costs and expenses			(16.6)	(40.2)	(94.1)
Reclassification out of Accumulated Other Comprehensive Income | Fuel and explosives commodity swaps | Cash flow hedges
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating costs and expenses			(11.0)	(22.2)	(47.0)
Reclassification out of Accumulated Other Comprehensive Income | Insignificant items | Cash flow hedges
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Insignificant items			(0.1)	(0.1)	(0.3)
Postretirement health care and life insurance benefits | Reclassification out of Accumulated Other Comprehensive Income | Net actuarial loss associated with postretirement plans and workers' compensation obligations
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating costs and expenses			(5.5)	(5.1)	(10.2)
Postretirement health care and life insurance benefits | Reclassification out of Accumulated Other Comprehensive Income | Prior service credit associated with postretirement plans
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating costs and expenses			2.3	2.8	5.5
Defined benefit pension plans | Reclassification out of Accumulated Other Comprehensive Income | Net actuarial loss associated with postretirement plans and workers' compensation obligations
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating costs and expenses			(5.3)	(5.1)	(10.2)
Selling and administrative expenses			(1.0)	(1.1)	(2.1)
Defined benefit pension plans | Reclassification out of Accumulated Other Comprehensive Income | Prior service credit associated with postretirement plans
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating costs and expenses			$ (0.1)	$ (0.1)	$ (0.2)