Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Common Share
Net income (loss)	$ 264.9	$ 319.2	$ 694.0	$ 643.3
Subtract:
Net income (loss) attributable to noncontrolling interest	7.3	4.6	14.0	26.8
Preferred stock dividends	8.3	8.3	16.5	16.5
Excess of redemption value over carrying value of preferred shares redeemed	8.2		8.2
Adjustments to redemption amounts of redeemable noncontrolling interests		(0.3)		9.4
Total	$ 241.1	$ 306.6	$ 655.3	$ 590.6
Weighted-average shares outstanding
Basic	295.0	294.7	294.9	295.2
Dilutive effects:
Stock options	1.6	1.7	1.6	1.7
Restricted stock units	1.5	1.5	1.6	1.7
Performance share awards	0.3	0.4	0.3	0.4
Diluted	298.4	298.3	298.4	299.0
Net income (loss) per common share:
Basic	$ 0.82	$ 1.04	$ 2.22	$ 2.00
Diluted	$ 0.81	$ 1.03	$ 2.20	$ 1.98