Segment Information - Reconciliation (Details ) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Oct. 31, 2020	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Depreciation and amortization			$ (4,710)	$ (4,829)	$ (5,120)
Goodwill impairment	$ (2,600)	$ (6,500)	(2,642)	(6,506)	(2,726)
Share-based compensation			(175)	(162)	(186)
OPERATING INCOME (LOSS)			962	(2,726)	570
Total other expense, net			(1,744)	(2,040)	(2,133)
LOSS BEFORE INCOME TAX EXPENSE			(782)	(4,766)	(1,563)
Income tax expense			450	503	170
Net loss			(1,232)	(5,269)	(1,733)
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment adjusted EBITDA			15,164	15,795	16,472
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Depreciation and amortization			(4,710)	(4,829)	(5,120)
Goodwill impairment			(2,642)	(6,506)	(2,726)
Other operating expenses			(6,675)	(7,024)	(7,870)
Share-based compensation			(175)	(162)	(186)
OPERATING INCOME (LOSS)			962	(2,726)	570
Total other expense, net			$ (1,744)	$ (2,040)	$ (2,133)