Segment Information (Details 3) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total reportable segment income	$ 487	$ 593	$ 1,485	$ 1,928
Depreciation and amortization	(910)	(995)	(2,739)	(2,958)
Other operating expenses	(3,547)	(3,789)	(10,848)	(11,253)
Total other expense, net	(348)	(344)	(999)	(982)
INCOME BEFORE INCOME TAX EXPENSE	139	249	486	946
Income tax expense	(47)	(97)	(214)	(362)
Net income	92	152	272	584
Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total reportable segment income	1,645	1,848	5,223	5,767
Segment reconciling items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Non-reportable segment revenues	173	162	497	486
Other operating revenues	303	304	893	919
Depreciation and amortization	(910)	(995)	(2,739)	(2,958)
Other operating expenses	(724)	(726)	(2,389)	(2,286)
Total other expense, net	$ (348)	$ (344)	$ (999)	$ (982)