CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH PROVIDED BY OPERATIONS:
Net income (loss)	$ 320.6	$ 93.3	$ (114.9)
Adjustments to reconcile net income (loss) to net cash provided by operations:
Depreciation and amortization	402.9	392.7	322.6
Provision for pension and postretirement benefits	15.0	34.0	25.1
Share-based compensation expense	34.6	33.6	34.5
(Gain) loss on disposals of property and equipment	8.7	(7.7)	(3.7)
Deferred income taxes	(37.9)	(1.1)	(182.5)
Contingent payment derivative	(6.1)	0.0	0.0
Asset impairment charges	34.3	329.8	574.0
Other	3.7	0.5	0.0
Changes in current assets and liabilities:
Receivables - trade and other	109.2	134.7	(200.6)
Prepaid expenses and other current assets	9.2	0.6	16.3
Accounts payable	(4.0)	23.2	(20.6)
Accrued income taxes	(3.4)	10.6	4.9
Other current liabilities	(32.2)	(13.1)	72.9
Other postretirement benefit claims paid	(7.9)	(4.4)	(4.1)
Contributions to pension plans	(22.5)	(11.4)	(54.8)
Deferred revenues	63.7	(3.1)	(18.3)
Net changes in other noncurrent assets and liabilities	12.7	(15.3)	(27.8)
Net cash provided by (used in) operations	900.6	996.9	423.0
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(117.6)	(722.9)	(1,958.2)
Proceeds from disposals of property and equipment	6.2	19.4	22.0
Net cash provided by (used in) investing activities	(111.4)	(703.5)	(1,936.2)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from borrowings	500.0	220.0	793.4
Reduction of long-term debt	(511.8)	(317.9)	0.0
Dividends paid	0.0	(50.5)	(37.7)
Debt issue costs	(8.7)	0.0	(0.7)
Proceeds from exercise of share options	0.0	0.0	4.7
Excess tax benefits from share-based compensation	2.6	0.0	(0.1)
Net cash provided by (used in) financing activities	(17.9)	(148.4)	759.6
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	771.3	145.0	(753.6)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	484.2	339.2	1,092.8
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 1,255.5	$ 484.2	$ 339.2