Common Shareholders' Equity (Earnings Per Share) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Reconciliation of basic and diluted earnings per share of common stock [Abstract]
Income from continuing operations	$ 84		$ 461
Denominator:
Weighted-average number of common shares outstanding - basic (in shares)	421.0		412.3
Performance share awards, options, restricted stock and equity units (in shares)	2.7	[1]	2.4	[1]
Weighted-average number of common shares outstanding - assuming dilution (in shares)	423.7		414.7
Earnings per share of common stock from continuing operations:
Basic	$ 0.20		$ 1.12
Assuming dilution	$ 0.20		$ 1.11
Antidilutive securities (in shares)	0.4		0.6

[1] Performance share awards are included in diluted weighted-average number of common shares outstanding based upon what would be issued if the end of the reporting period was the end of the term of the award. Performance share awards, options, equity units and restricted stock are included in diluted weighted-average number of common shares outstanding by applying the treasury stock method.