Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
OPERATING ACTIVITIES
Net income	$ 798	$ 701
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	483	463
Deferred income taxes	145	137
Long-term casualty and environmental liabilities, net	(17)	(46)
Contribution to defined benefit pension plan	(25)	(36)
Other, net	(37)	(29)
Changes in current assets and liabilities:
Accounts receivable, net	(81)	47
Materials and supplies	(38)	(97)
Other current assets	(74)	(76)
Accounts payable and other current liabilities	(242)	15
Net cash provided by operating activities	912	1,079
INVESTING ACTIVITIES
Capital expenditures excluding equipment	(546)	(528)
Acquisition of equipment	(186)	(298)
Other, net	(21)	(130)
Net cash used for investing activities	(753)	(956)
FINANCING ACTIVITIES
Proceeds from issuance of long-term debt	1,500	1,250
Payments on long-term debt	(58)	(46)
Cash distributions	(1,000)	(1,000)
Other, net	(10)	(11)
Net cash provided by financing activities	432	193
Increase in cash and cash equivalents	591	316
Cash and cash equivalents:
Beginning of period	1,794	1,960
End of period	2,385	2,276
SUPPLEMENTAL CASH FLOW INFORMATION
Interest paid, net of amounts capitalized	229	189
Capital investments accrued but not yet paid	104	118
Income taxes paid, net of refunds	$ 288	$ 28