Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Accounts receivable, allowances	$ 62	$ 65
Property and equipment, accumulated depreciation	2,783	2,568
Identifiable intangible assets, accumulated amortization	$ 981	$ 909
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	1,000.000
Preferred stock, shares outstanding (in shares)	0	1,000.000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	112,000,000	102,000,000
Common stock, shares outstanding (in shares)	112,000,000	102,000,000