Consolidated Balance Sheets - (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable allowances	$ 58	$ 52
Property and equipment, accumulated depreciation	2,054	1,585
Identifiable intangible assets, accumulated amortization	$ 850	$ 706
Preferred stock, par value (in usd 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 usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	92,000,000	116,000,000
Common stock, shares outstanding (in shares)	92,000,000	116,000,000