Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Common Share
Net income (loss)	$ 369.2	$ 429.1
Subtract:
Net income (loss) attributable to noncontrolling interest	1.2	6.7
Preferred stock dividends		8.2
Total	$ 368.0	$ 414.2
Weighted-average shares outstanding
Basic	291.5	294.8
Dilutive effects:
Stock options	1.0	1.7
Restricted stock units	1.6	1.8
Performance share awards	0.2	0.2
Diluted	294.3	298.5
Net income (loss) per common share:
Basic	$ 1.26	$ 1.41
Diluted	$ 1.25	$ 1.39