Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating activities:
Net income	$ 104.2	$ 75.3
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	53.1	48.4
Deferred income taxes	22.1	34.9
Equity in net earnings of unconsolidated affiliates	(5.5)	(5.8)
Share-based compensation	4.6	3.2
Excess tax benefit from share-based compensation	(2.9)	(13.2)
Deferred compensation	0	7.3
Debt retirement costs	0	12.9
Changes in working capital items:
Accounts receivable	(18.7)	(21.1)
Materials and supplies	(13.1)	(11.5)
Other current assets	5.2	4.8
Accounts payable and accrued liabilities	(25.4)	0.2
Other, net	2.0	4.1
Net cash provided by operating activities	125.6	139.5
Investing activities:
Capital expenditures	(112.7)	(99.4)
Property investments in MSLLC	(12.9)	(6.7)
Proceeds from disposal of property	2.9	2.7
Other, net	(0.1)	2.3
Net cash used for investing activities	(122.8)	(101.1)
Financing activities:
Proceeds from issuance of long-term debt	0	229.6
Repayment of long-term debt	(14.5)	(237.0)
Debt costs	(0.5)	(15.0)
Proceeds from employee stock plans	0.4	0.3
Excess tax benefit from share-based compensation	2.9	13.2
Dividends paid	0	(0.1)
Net cash used for financing activities	(11.7)	(9.0)
Cash and cash equivalents:
Net increase (decrease) during each period	(8.9)	29.4
At beginning of year	72.6	72.4
At end of period	$ 63.7	$ 101.8