Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Activities [Abstract]
Net income	$ 4,388	$ 3,943	$ 3,292
Adjustments to reconcile net income to cash provided by operating activities [Abstract]
Depreciation	1,777	1,760	1,617
Deferred income taxes and unrecognized tax benefits	723	887	986
Other operating activities, net	(226)	(160)	(298)
Changes in current assets and liabilities [Abstract]
Accounts receivable, net	(83)	70	(217)
Materials and supplies	7	(46)	(80)
Other current assets	74	(108)	178
Accounts payable and other current liabilities	163	(185)	395
Cash provided by operating activities	6,823	6,161	5,873
Investing Activities [Abstract]
Capital investments	(3,496)	(3,738)	(3,176)
Proceeds from asset sales	98	80	108
Acquisition of equipment pending financing	0	(274)	(85)
Proceeds from sale of assets financed	0	274	85
Other investing activities, net	(7)	25	(51)
Cash used in investing activities	(3,405)	(3,633)	(3,119)
Financing Activities [Abstract]
Common share repurchases (Note 18)	(2,218)	(1,474)	(1,418)
Debt issued	1,443	695	486
Dividends paid	(1,333)	(1,146)	(837)
Debt repaid	(640)	(758)	(690)
Debt exchange	(289)	0	(272)
Other financing activities, net	(12)	1	108
Cash used in financing activities	(3,049)	(2,682)	(2,623)
Net change in cash and cash equivalents	369	(154)	131
Cash and cash equivalents at beginning of year	1,063	1,217	1,086
Cash and cash equivalents at end of year	1,432	1,063	1,217
Non-cash investing and financing activities [Abstract]
Cash dividends declared but not yet paid	356	318	284
Capital investments accrued but not yet paid	133	136	147
Capital lease financings	39	290	154
Cash paid during the year for: [Abstract]
Interest, net of amounts capitalized	(528)	(561)	(572)
Income taxes, net of refunds	$ (1,656)	$ (1,552)	$ (625)