Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 105.5	$ 72.4
Accounts receivable, net	184.8	166.0
Materials and supplies	117.3	109.6
Deferred income taxes	164.6	225.0
Other current assets	55.2	69.5
Total current assets	627.4	642.5
Investments	54.5	50.4
Restricted funds	11.8	21.7
Property and equipment (including concession assets), net	5,479.1	5,349.5
Other assets	118.0	108.9
Total assets	6,290.8	6,173.0
Current liabilities:
Debt due within one year	52.2	36.3
Accounts payable and accrued liabilities	393.2	401.1
Total current liabilities	445.4	437.4
Long-term debt	1,570.7	1,602.8
Deferred income taxes	868.1	861.4
Other noncurrent liabilities and deferred credits	174.2	212.7
Total liabilities	3,058.4	3,114.3
Commitments and contingencies	0	0
Stockholders' equity:
$.01 par, common stock, 400,000,000 shares authorized; 123,352,185 shares issued; 110,011,041 and 109,910,857 shares outstanding at June 30, 2012 and December 31, 2011, respectively	1.1	1.1
Paid-in capital	905.0	884.2
Retained earnings	2,027.7	1,875.3
Accumulated other comprehensive loss	(2.5)	(2.2)
Total stockholders’ equity	2,937.4	2,764.5
Noncontrolling interest	295.0	294.2
Total equity	3,232.4	3,058.7
Total liabilities and equity	6,290.8	6,173.0
$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