Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Allowances for accounts receivable, current	$ 99	$ 69
Common stock, par value (in dollars per share)	$ 0.25	$ 0.25
Common stock, shares authorized (in shares)	175,000,000	175,000,000
Common stock, shares issued (in shares)	80,367,000	79,532,000
Common stock, shares outstanding (in shares)	80,251,000	78,441,000
Series A Preferred Stock [Member]
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	50,000,000	50,000,000
Preferred Stock, Dividend Rate, Percentage	11.125%	11.125%
Preferred Stock, Shares Issued	19,250,000	19,250,000
Preferred Stock, Shares Outstanding	19,250,000	19,250,000