Shareholders' Equity and Earnings per Common Share - Calculation of Basic and Diluted Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Equity [Abstract]
Net income (loss)	$ 517.4	$ 447.7	$ 1,201.9	$ 136.9
Less: Net income (loss) attributable to noncontrolling interest	116.6	101.1	296.7	84.5
Net income (loss) available to common shareholders	$ 400.8	$ 346.6	$ 905.2	$ 52.4
Weighted-average common shares outstanding, Basic:
Basic	252.6	260.8	256.0	247.1
Weighted-average common shares outstanding, Dilutive Effects:
Dilutive	254.4	262.3	258.1	247.8
Net income (loss) per common share
Basic	$ 1.59	$ 1.33	$ 3.54	$ 0.21
Diluted	$ 1.58	$ 1.32	$ 3.51	$ 0.21
Restricted Stock Units (RSUs)
Weighted-average common shares outstanding, Dilutive Effects:
Dilutive effects of share-based payments	1.5	0.7	1.2	0.3
Performance shares (PSU awards)
Weighted-average common shares outstanding, Dilutive Effects:
Dilutive effects of share-based payments	0.3	0.2	0.4	0.1
RSUs - Deal incentive awards
Weighted-average common shares outstanding, Dilutive Effects:
Dilutive effects of share-based payments	0	0.6	0.5	0.3