Common Equity Common Equity 2 (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Stock options [Member]	Sep. 30, 2012 Stock options [Member]	Sep. 30, 2011 Stock options [Member]	Mar. 31, 2012 Stock options [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number						10,638,750		9,571,531
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period					0	938,770	458,180
Share Based Compensation Arrangement By Share Based Payment Award Options Grant In Period Weighted Average Exercise Price					$ 0.00	$ 34.88
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period					(370,020)	(2,368,289)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period					0	(7,720)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	9,201,511		9,201,511		9,201,511	9,201,511		9,571,531
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price						$ 21.65		$ 23.42
Share Based Compensation Arrangement By Share Based Payment Awards Options Exercises In Period Weighted Average Exercise Price					$ 17.89	$ 19.11
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price					$ 0.00	$ 26.94
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 23.65		$ 23.65		$ 23.65	$ 23.65		$ 23.42
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Outstanding Options Weighted Average Remaining Contractual Period						5 years 5 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value					$ 129.0	$ 129.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	7,493,036		7,493,036		7,493,036	7,493,036
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	$ 21.98		$ 21.98		$ 21.98	$ 21.98
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Remaining Contractual Term			4 years 8 months			4 years 8 months
Share Based Compensation Arrangement by Share Based Payments Award, Options Exercisable, Intrinsic Value					117.6	117.6
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	8.3	3.6	42.1	22.6
Exercise of stock options			45.3	34.4
Tax Benefit from Stock Options Exercised			$ 0	$ 9.0