CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Allowance for uncollectible accounts	$ 6	$ 7
Common stock, par value per share	$ 0.1	$ 0.1
Common stock, shares authorized	1,000,000,000.0	1,000,000,000.0
Common stock, shares issued	527,700,000	525,900,000
Treasury stock, shares	19,700,000	19,300,000