Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Receivables, allowances for uncollectible accounts	$ 76	$ 75
Utility property, plant and equipment, accumulated depreciation	7,088	6,894
Nonutility property, plant and equipment, accumulated depreciation	$ 110	$ 107
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized	560,000,000	560,000,000
Common stock, shares issued	434,888,104	434,888,104
Common stock, shares outstanding	434,888,104	434,888,104