Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 285.8	$ 429.5
Accounts receivable, net	208.5	198.3
Materials and supplies	122.8	121.3
Deferred income taxes	115.4	131.6
Other current assets	47.8	61.7
Total current assets	780.3	942.4
Investments	43.3	41.1
Restricted funds	0	4.2
Property and equipment (including concession assets), net	6,909.4	6,356.3
Other assets	84.0	91.4
Total assets	7,817.0	7,435.4
Current liabilities:
Debt due within one year	24.8	332.0
Commercial paper	312.0	0
Accounts payable and accrued liabilities	424.1	398.6
Total current liabilities	760.9	730.6
Long-term debt	1,846.1	1,856.9
Deferred income taxes	1,128.0	1,044.6
Other noncurrent liabilities and deferred credits	128.9	126.7
Total liabilities	3,863.9	3,758.8
Commitments and contingencies	0	0
Stockholders' equity:
$.01 par, common stock, 400,000,000 shares authorized; 123,352,185 shares issued; 110,360,558 and 110,229,229 shares outstanding at September 30, 2014 and December 31, 2013, respectively	1.1	1.1
Additional paid-in capital	949.6	942.5
Retained earnings	2,691.6	2,422.9
Accumulated other comprehensive loss	(2.3)	(2.0)
Total stockholders’ equity	3,646.1	3,370.6
Noncontrolling interest	307.0	306.0
Total equity	3,953.1	3,676.6
Total liabilities and equity	7,817.0	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