Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
OPERATING ACTIVITIES
Net income	$ 724	$ 798
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	515	483
Deferred income taxes	61	145
Long-term casualty and environmental liabilities, net	(9)	(17)
Contribution to defined benefit pension plan	0	(25)
Other, net	(217)	(37)
Changes in current assets and liabilities:
Accounts receivable, net	(9)	(81)
Materials and supplies	(24)	(38)
Other current assets	(66)	(74)
Accounts payable and other current liabilities	172	(242)
Net cash provided by operating activities	1,147	912
INVESTING ACTIVITIES
Capital expenditures excluding equipment	(645)	(546)
Acquisition of equipment	(273)	(186)
Other, net	(96)	(21)
Net cash used for investing activities	(1,014)	(753)
FINANCING ACTIVITIES
Proceeds from issuance of long-term debt	1,500	1,500
Payments on long-term debt	(538)	(58)
Cash distributions	(750)	(1,000)
Other, net	(15)	(10)
Net cash provided by financing activities	197	432
Increase in cash and cash equivalents	330	591
Cash and cash equivalents:
Beginning of period	2,225	1,794
End of period	2,555	2,385
SUPPLEMENTAL CASH FLOW INFORMATION
Interest paid, net of amounts capitalized	277	229
Capital investments accrued but not yet paid	119	104
Income taxes paid, net of refunds	$ 34	$ 288