Income Taxes (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended			9 Months Ended
	Mar. 31, 2013	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Jan. 31, 2013	Dec. 31, 2012
Differences in the expected income tax provision based on statutory rates applied to earnings before income taxes and the income tax provision reflected in the consolidated statements of operations
Income tax provision		$ 109.0		$ 206.0	$ 499.3	$ 722.0
Pre-tax income		345.7		640.2	1,684.5	2,241.3
Differences in the expected income tax provision based on statutory rates applied to earnings before income taxes and the income tax provision reflected in the consolidated statements of operations (as a percent)
Effective income tax rate (as a percent)		31.50%		32.20%
Income tax benefit included in income tax provision fully reserved by valuation allowance								94.3
Percentage of retention of any settlement realized with the United States Internal Revenue Service (IRS) at the IRS Appeals level							26.90%
Period of entitlement of tax deduction equal to portion of NOL commencing with 2012 year	5 years
Percentage of federal and state tax savings payable to pre-IPO owners	73.10%		73.10%
Tax savings payable to pre-IPO owners	55.2		55.2
Current portion of the tax savings payable to the pre-IPO owners		13.5			13.5
Non current portion of the tax savings payable to the pre-IPO owners		41.7			41.7
Decrease in unrecognized tax benefits			86.8
Portion of unrecognized tax benefits, if recognized, would affect the effective tax rate		$ 75.3			$ 75.3