Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 348.0	$ 429.5
Accounts receivable, net	181.6	198.3
Materials and supplies	111.0	121.3
Deferred income taxes	100.1	131.6
Other current assets	77.6	61.7
Total current assets	818.3	942.4
Investments	36.4	41.1
Property and equipment (including concession assets), net	7,154.7	6,356.3
Other assets	81.6	95.6
Total assets	8,091.0	7,435.4
Current liabilities:
Long-term debt due within one year	24.8	332.0
Short-term borrowings	450.1	0
Accounts payable and accrued liabilities	423.9	398.6
Total current liabilities	898.8	730.6
Long-term debt	1,841.0	1,856.9
Deferred income taxes	1,156.3	1,044.6
Other noncurrent liabilities and deferred credits	130.8	126.7
Total liabilities	4,026.9	3,758.8
Commitments and contingencies	0	0
Stockholders’ equity:
$.01 par, common stock, 400,000,000 shares authorized, 123,352,185 shares issued; 110,392,330 and 110,229,229 shares outstanding at December 31, 2014 and 2013, respectively	1.1	1.1
Additional paid-in capital	949.8	942.5
Retained earnings	2,801.7	2,422.9
Accumulated other comprehensive loss	(3.2)	(2.0)
Total stockholders’ equity	3,755.5	3,370.6
Noncontrolling interest	308.6	306.0
Total equity	4,064.1	3,676.6
Total liabilities and equity	8,091.0	7,435.4
$25 Par Preferred Stock [Member]
Stockholders’ equity:
$25 par, 4% noncumulative, preferred stock, 840,000 shares authorized, 649,736 shares issued, 242,170 shares outstanding	$ 6.1	$ 6.1