Summary Of Significant Accounting Policies (Earnings Per Common Share) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Summary Of Significant Accounting Policies [Abstract]
Net income for common stock	$ 277	$ 311
Weighted average common shares outstanding - Basic	292.9	292.0
Add: Incremental shares attributable to effect of potentially dilutive securities	1.6	1.6
Adjusted weighted average common shares outstanding - Diluted	294.5	293.6
Net income for common stock per common share - basic	$ 0.95	$ 1.07
Net income for common stock per common share - diluted	$ 0.94	$ 1.06