Consolidated Balance Sheets Parentheticals (Parentheticals) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts	$ 33	$ 32
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ 10,625	$ 10,365
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	$ 0.01	$ 0.01
Common stock, shares authorized	433,333,333	433,333,333
Common stock, shares issued	357,005,439	356,374,473
Common stock, shares outstanding	357,005,439	356,374,473