Segment Information - Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Total segment adjusted EBITDA	$ 2,112	$ 2,223		$ 6,406	$ 6,666
Depreciation and amortization	(1,193)	(1,235)		(3,515)	(3,619)
Impairment of goodwill	0	0	$ (6,500)	0	(6,506)
Total other expense, net	(408)	(540)		(1,345)	(1,542)
INCOME (LOSS) BEFORE INCOME TAXES	480	410		1,426	(5,115)
Income tax expense	114	108		369	377
Net income (loss)	366	302		1,057	(5,492)
Operating segments
Segment Reporting Information [Line Items]
Total segment adjusted EBITDA	3,786	3,940		11,398	11,855
Segment Reconciling Items
Segment Reporting Information [Line Items]
Total segment adjusted EBITDA	(1,674)	(1,717)		(4,992)	(5,189)
Depreciation and amortization	(1,193)	(1,235)		(3,515)	(3,619)
Impairment of goodwill	0	0		0	(6,506)
Other operating expenses	(1,674)	(1,717)		(4,992)	(5,189)
Stock-based compensation	(31)	(38)		(120)	(114)
Operating income (loss)	888	950		2,771	(3,573)
Total other expense, net	$ (408)	$ (540)		$ (1,345)	$ (1,542)