Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash Flows From Operating Activities
Net income (loss)	$ 120.2	$ (171.1)
Loss from discontinued operations, net of income taxes	4.1	3.4
Loss from continuing operations, net of income taxes	124.3	(167.7)
Adjustments to reconcile loss from continuing operations, net of income taxes to net cash used in operating activities:
Depreciation, depletion and amortization	119.9	111.8
Noncash interest expense	0.5	6.9
Deferred income taxes	1.7	(43.4)
Noncash share-based compensation	1.9	2.4
Asset impairment	30.5	17.2
Net gain on disposal of assets	(22.8)	(1.8)
(Income) loss from equity affiliates	(15.0)	9.0
Gain on VEBA settlement	0.0	(68.1)
Settlement of hedge positions	0.0	(17.8)
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	0.0	25.0
Reclassification from OCI for terminated hedge contracts	27.6	0.0
Noncash reorganization items, net	10.0	0.0
Changes in current assets and liabilities:
Accounts receivable	159.3	125.8
Change in receivable from accounts receivable securitization program	0.0	(168.5)
Inventories	(47.2)	(8.0)
Net assets from coal trading activities	(0.5)	6.0
Other current assets	0.1	(36.0)
Accounts payable and accrued expenses	(54.9)	(71.1)
Restricted cash	(94.1)	(100.2)
Asset retirement obligations	10.2	9.0
Workers' Compensation Liabilities	(3.1)	(3.3)
Accrued postretirement benefit costs	0.8	(0.2)
Accrued pension costs	5.4	5.4
Take-or-pay obligation settlement	(5.5)	(15.5)
Other, net	(2.5)	(5.8)
Net Cash (Used in) Provided by Operating Activities, Continuing Operations	246.6	(438.9)
Net cash used in discontinued operations	(8.2)	(0.1)
Net Cash (Used in) Provided by Operating Activities	238.4	(439.0)
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development	(32.8)	(13.3)
Changes in accrued expenses related to capital expenditures	(1.4)	(3.4)
Increase (Decrease) in Due from Related Parties	31.1	2.1
Federal coal lease expenditures	(0.5)	(0.4)
Proceeds from disposal of assets, net of notes receivable	24.3	2.1
Contributions to joint ventures	(95.4)	(81.7)
Distributions from joint ventures	90.5	87.4
Increase (Decrease) in Due to Related Parties	(0.4)	(1.2)
Other, net	(0.3)	(4.5)
Net cash (used in) provided by investing activities	15.1	(12.9)
Cash Flows From Financing Activities
Proceeds from long-term debt	1,000.0	947.0
Restricted Cash Related to Proceeds from Long-term Debt	(1,000.0)	0.0
Repayments of long-term debt	(2.1)	(6.2)
Payment of deferred financing costs	(55.4)	(2.8)
Distributions to noncontrolling interests	(0.1)	0.0
Other, net	(0.1)	(1.8)
Net cash provided by financing activities	(57.7)	936.2
Net change in cash and cash equivalents	195.8	484.3
Cash and cash equivalents at beginning of period	872.3	261.3
Cash and cash equivalents at end of period	1,068.1	$ 745.6
Net Cash Provided by (Used in) Investing Activities, Continuing Operations	$ 15.1