Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Accounts receivable, allowances	$ 63	$ 58
Property and equipment, accumulated depreciation	2,138	2,054
Identifiable intangible assets, accumulated amortization	$ 825	$ 850
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)	70,000	70,000
Preferred stock, shares outstanding (in shares)	70,000	70,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	300,000,000.0	300,000,000.0
Common stock, shares issued (in shares)	91,000,000	92,000,000
Common stock, shares outstanding (in shares)	91,000,000	92,000,000