Equity - Common Stock (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jan. 12, 2009
Common Stock [Details]
Common shares, authorized	500	500
Common shares, outstanding	295	293
Total issuances - shares	2.0	12.2	17.5
Issuance under an underwritten public offering - shares	0	0	14.4
Issuance through 401(k) and or IPP - shares	0	11.2	2.5
Total issuances - net proceeds	$ 53	$ 434	$ 623
Issuances under an underwritten public offering - net proceeds	0	0	523
Issuances through 401(k) and or IPP - net proceeds	$ 1	$ 431	$ 100
Public Offering Price Per Share				$ 37.50