Share-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Share-based compensation disclosures
Share Based Compensation expense	$ 32.9	$ 4.5
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	4,414,960	907,786
Vesting period of shares	4 years
Shares awarded during period, fair value	71.9	19.0
Fair value of Restricted Stock Awarded to Employees and Directors that vested	35.5	8.2
Stock options
Share-based compensation disclosures
Vesting period of shares	4 years	4 years
Total intrinsic value of stock options exercised	0.7	4.9
Intrinsic value of stock options surrendered		17.9
Total fair value of options vested during the period	$ 3.8	$ 7.5
Options awarded (in shares)	37,825	621,000
Fair value of stock options
Weighted-average fair value of options granted (in dollars per share)	$ 15.96	$ 22.20
Weighted-average risk free interest rate (as a percent)	0.57%	0.64%
Dividend yield (as a percent)	0.74%	0.00%
Volatility (as a percent)	51.01%	56.02%
Expected life	4 years	4 years