Consolidated Balance Sheets Parentheticals (Parentheticals) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts	$ 30	$ 29
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ 11,534	$ 11,249
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	433,333,333	433,333,333
Common stock, shares issued	360,856,279	360,021,098
Common stock, shares outstanding	360,856,279	360,021,098