Earnings Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Common Share
Net income (loss)	$ 190.0	$ 221.3
Subtract:
Net income (loss) attributable to noncontrolling interest	3.5	9.2
Preferred stock dividends	8.2	8.2
Net income (loss) available to common stockholders	$ 178.3	$ 203.9
Weighted-average shares outstanding
Basic	294.1	301.8
Dilutive effects:
Stock options	1.1	1.0
Restricted stock units	1.7	1.6
Performance share awards	0.2	0.3
Diluted	297.1	304.7
Net income (loss) per common share:
Basic	$ 0.61	$ 0.68
Diluted	$ 0.61	$ 0.68