Segment Information (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment income	$ 549	$ 655	$ 1,198	$ 1,308
Depreciation and amortization	(1,048)	(1,093)	(2,088)	(2,200)
Other unassigned operating expenses	(863)	(831)	(1,714)	(1,674)
Other income (expense), net	(315)	(332)	(641)	(654)
Income tax expense	(91)	(130)	(222)	(258)
Net income	143	193	335	396
Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment income	2,019	2,171	4,140	4,359
Segment reconciling items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other operating revenues	258	253	515	507
Depreciation and amortization	(1,048)	(1,093)	(2,088)	(2,200)
Other unassigned operating expenses	(680)	(676)	(1,369)	(1,358)
Other income (expense), net	(315)	(332)	(641)	(654)
Income tax expense	$ (91)	$ (130)	$ (222)	$ (258)