Segment Information - Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Total segment adjusted EBITDA	$ 2,215		$ 2,111	$ 4,443	$ 4,185
Depreciation and amortization	(1,196)		(1,290)	(2,384)	(2,573)
Impairment of goodwill	0	$ (6,500)	0	(6,506)	0
Stock-based compensation	(43)		(54)	(76)	(95)
Total other expense, net	(474)		(530)	(1,002)	(1,044)
INCOME (LOSS) BEFORE INCOME TAXES	502		237	(5,525)	473
Income tax expense (benefit)	(131)		55	(269)	(66)
NET INCOME (LOSS)	371		292	(5,794)	407
Operating segments
Segment Reporting Information [Line Items]
Total segment adjusted EBITDA	3,992		4,197	8,025	8,363
Segment Reconciling Items
Segment Reporting Information [Line Items]
Total segment adjusted EBITDA	(1,777)		(2,086)	(3,582)	(4,178)
Depreciation and amortization	(1,196)		(1,290)	(2,384)	(2,573)
Impairment of goodwill	0		0	(6,506)	0
Other operating expenses	(1,777)		(2,086)	(3,582)	(4,178)
Operating income (loss)	976		767	(4,523)	1,517
Total other expense, net	$ (474)		$ (530)	$ (1,002)	$ (1,044)