CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Allowance for uncollectible accounts	$ 6	$ 7
Common stock, par value	$ 0.1	$ 0.1
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	521,700,000	518,600,000
Treasury stock, shares	18,500,000	18,100,000