Segment Information (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total reportable segment income	$ 367	$ 647	$ 998	$ 1,335
Depreciation and amortization	(949)	(987)	(1,829)	(1,963)
Other operating expenses	(3,723)	(3,751)	(7,301)	(7,464)
Total other expense, net	(327)	(330)	(651)	(638)
INCOME BEFORE INCOME TAX EXPENSE	40	317	347	697
Income tax expense	(23)	(121)	(167)	(265)
Net income	17	196	180	432
Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total reportable segment income	1,740	1,918	3,578	3,919
Segment reconciling items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Non-reportable segment revenues	171	162	324	324
Other operating revenues	302	307	590	615
Depreciation and amortization	(949)	(987)	(1,829)	(1,963)
Other operating expenses	(897)	(753)	(1,665)	(1,560)
Total other expense, net	$ (327)	$ (330)	$ (651)	$ (638)