Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 190.2	$ 429.5
Accounts receivable, net	213.1	198.3
Materials and supplies	125.8	121.3
Deferred income taxes	123.3	131.6
Other current assets	55.8	61.7
Total current assets	708.2	942.4
Investments	38.9	41.1
Restricted funds	0	4.2
Property and equipment (including concession assets), net	6,825.8	6,356.3
Other assets	77.8	91.4
Total assets	7,650.7	7,435.4
Current liabilities:
Debt due within one year	24.8	332.0
Commercial paper	321.0	0
Accounts payable and accrued liabilities	383.2	398.6
Total current liabilities	729.0	730.6
Long-term debt	1,852.4	1,856.9
Deferred income taxes	1,097.9	1,044.6
Other noncurrent liabilities and deferred credits	129.6	126.7
Total liabilities	3,808.9	3,758.8
Commitments and contingencies	0	0
Stockholders' equity:
$.01 par, common stock, 400,000,000 shares authorized; 123,352,185 shares issued; 110,323,832 and 110,229,229 shares outstanding at June 30, 2014 and December 31, 2013, respectively	1.1	1.1
Additional paid-in capital	945.4	942.5
Retained earnings	2,584.5	2,422.9
Accumulated other comprehensive loss	(2.0)	(2.0)
Total stockholders’ equity	3,535.1	3,370.6
Noncontrolling interest	306.7	306.0
Total equity	3,841.8	3,676.6
Total liabilities and equity	7,650.7	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