Condensed Consolidated Balance Sheet (Parenthetical) - USD ($) shares in Millions, $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accumulated depreciation, property and equipment	$ 7,760	$ 7,500
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	20	20
Preferred Stock, Shares Issued	2	2
Preferred Stock, Shares Outstanding	2	2
Preferred Stock, Liquidation Preference, Value	$ 1,650	$ 1,650
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	600	600
Common stock, shares outstanding	415	406