Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Millions	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Cash Flows From Operating Activities
Net income	$ 752.4	$ 587.2
Loss from discontinued operations, net of income taxes	3.7	2.2
Income from continuing operations, net of income taxes	756.1	589.4
Adjustments to reconcile income from continuing operations, net of income taxes to net cash provided by operating activities:
Depreciation, depletion and amortization	327.8	327.3
Deferred income taxes	49.1	178.6
Share-based compensation	32.4	30.1
Net gain on disposal or exchange of assets	(31.4)	(15.4)
Loss (income) from equity affiliates	9.0	(2.1)
Changes in current assets and liabilities:
Accounts receivable	(12.5)	(124.3)
Accounts receivable securitization program	0	(154.6)
Inventories	(17.5)	(71.2)
Net assets from coal trading activities	71.7	(0.8)
Other current assets	(41.6)	19.9
Accounts payable and accrued expenses	(8.6)	116.5
Asset retirement obligations	27.8	20.3
Workers' compensation obligations	0.3	5.6
Pension costs	25.5	17.5
Accrued postretirement benefit costs	26.6	18.4
Contributions to pension plans	(1.3)	(23.9)
Other, net	(19.3)	(27.8)
Net cash provided by continuing operations	1,194.1	903.5
Net cash used in discontinued operations	(3.6)	(11.3)
Net cash provided by operating activities	1,190.5	892.2
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development	(616.2)	(291.3)
Federal coal lease expenditures	(42.4)	0
Investment in Prairie State Energy Campus	(29.8)	(52.5)
Proceeds from disposal of assets	12.1	9.7
Investments in equity affiliates and joint ventures	(39.8)	(18.8)
Proceeds from sales of debt and equity securities	53.3	10.6
Purchases of debt and equity securities	(44.1)	(73.6)
Purchases of short-term investments	(100.0)	0
Maturity of short-term investments	100.0	0
Investment in shares of Macarthur Coal Limited	(45.5)	0
Other, net	(4.4)	(7.4)
Net cash used in investing activities	(756.8)	(423.3)
Cash Flows From Financing Activities
Proceeds from long-term debt	1.4	1,150.0
Payments of long-term debt	(248.4)	(1,148.5)
Dividends paid	(69.1)	(56.5)
Repurchase of employee common stock relinquished for tax withholding	(16.1)	(8.4)
Payment of debt issuance costs	(4.0)	(32.2)
Excess tax benefits related to share-based compensation	6.1	0
Proceeds from stock options exercised	4.5	5.9
Other, net	(1.7)	(0.5)
Net cash used in financing activities	(327.3)	(90.2)
Net change in cash and cash equivalents	106.4	378.7
Cash and cash equivalents at beginning of period	1,295.2	988.8
Cash and cash equivalents at end of period	$ 1,401.6	$ 1,367.5