Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 187.0	$ 72.4
Accounts receivable, net	200.8	166.0
Materials and supplies	123.6	109.6
Deferred income taxes	135.7	225.0
Other current assets	35.3	69.5
Total current assets	682.4	642.5
Investments	59.7	50.4
Restricted funds	7.7	21.7
Property and equipment (including concession assets), net	5,551.6	5,349.5
Other assets	122.8	108.9
Total assets	6,424.2	6,173.0
Current liabilities:
Debt due within one year	51.8	36.3
Accounts payable and accrued liabilities	436.3	401.1
Total current liabilities	488.1	437.4
Long-term debt	1,557.0	1,602.8
Deferred income taxes	892.0	861.4
Other noncurrent liabilities and deferred credits	173.9	212.7
Total liabilities	3,111.0	3,114.3
Commitments and contingencies	0	0
Stockholders' equity:
$.01 par, common stock, 400,000,000 shares authorized; 123,352,185 shares issued; 110,044,355 and 109,910,857 shares outstanding at September 30, 2012 and December 31, 2011, respectively	1.1	1.1
Paid-in capital	916.5	884.2
Retained earnings	2,096.2	1,875.3
Accumulated other comprehensive loss	(2.3)	(2.2)
Total stockholders’ equity	3,017.6	2,764.5
Noncontrolling interest	295.6	294.2
Total equity	3,313.2	3,058.7
Total liabilities and equity	6,424.2	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