Segment Information (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment income	$ 649us-gaap_OperatingIncomeLoss	$ 653us-gaap_OperatingIncomeLoss
Depreciation and amortization	(1,040)us-gaap_DepreciationAndAmortization	(1,107)us-gaap_DepreciationAndAmortization
Other unassigned operating expenses	(851)	(843)
Other income (expense), net	(326)us-gaap_NonoperatingIncomeExpense	(322)us-gaap_NonoperatingIncomeExpense
Income tax expense	(131)us-gaap_IncomeTaxExpenseBenefit	(128)us-gaap_IncomeTaxExpenseBenefit
Net income	192us-gaap_NetIncomeLoss	203us-gaap_NetIncomeLoss
Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment income	2,121	2,188
Segment reconciling items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other operating revenues	257	254
Depreciation and amortization	1,040	(1,107)
Other unassigned operating expenses	689	682
Other income (expense), net	(326)	(322)
Income tax expense	$ 131	$ 128

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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