Share-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Share-based compensation disclosures
Share Based Compensation expense	$ 7.1	$ 4.8	$ 45.9	$ 13.5
Petrello
Share-based compensation disclosures
Value of incentives in the form of one-time stock grant			18.0
Common stock | Petrello
Share-based compensation disclosures
Value of incentives in the form of one-time stock grant			27.0
Restricted Stock Award
Share-based compensation disclosures
Shares awarded during period			4,729,193	934,648
Shares awarded during period, fair value			76.8	19.4
Fair value of Restricted Stock Awarded to Employees and Directors that vested			36.6	9.4
Restricted Stock Award | Maximum
Share-based compensation disclosures
Vesting period of shares			4 years
Stock options
Share-based compensation disclosures
Total intrinsic value of stock options exercised			3.2	5.7
Intrinsic value of stock options surrendered				17.9
Total fair value of options vested during the period			$ 4.0	$ 7.6
Options awarded (in shares)			53,672	653,699
Fair value of stock options
Weighted-average fair value of options granted (in dollars per share)			$ 6.21	$ 9.42
Weighted-average risk free interest rate (as a percent)			0.71%	0.63%
Dividend yield (as a percent)			0.82%	0.00%
Volatility (as a percent)			51.01%	55.77%
Expected life			4 years	4 years
Stock options | Maximum
Share-based compensation disclosures
Vesting period of shares			4 years	4 years