Employee Benefit Benefits and Stock-Based Compensation - Range of OSO Exercise Prices (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended							3 Months Ended	12 Months Ended			12 Months Ended
	Dec. 31, 2013 Outperform Stock Options	Dec. 31, 2012 Outperform Stock Options	Dec. 31, 2011 Outperform Stock Options	Dec. 31, 2010 Outperform Stock Options	Dec. 31, 2013 Outperform Stock Options Range, 14.10 to $20.85	Dec. 31, 2013 Outperform Stock Options Range, $22.05 to $24.30	Dec. 31, 2013 Outperform Stock Options Range, $27.53 to $36.60	Dec. 31, 2011 Non Qualified Stock Options	Dec. 31, 2013 Non Qualified Stock Options	Dec. 31, 2012 Non Qualified Stock Options	Oct. 04, 2011 Non Qualified Stock Options	Dec. 31, 2013 Non Qualified Stock Options Range, $14.43
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range
Options exercised, Weighted Average Initial Strike Price (in dollars per share)	$ 14.10	$ 12.48	$ 14.93					$ 10.93	$ 10.50	$ 10.61
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	2,148,865	2,066,419	1,288,712	1,056,392				598,190	26,665	62,324	765,585
Total realized value of OSO units	$ 1.5	$ 0.8	$ 0.4					$ 1.0	$ 1.0	$ 6.0
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options								2		5
OSO units Outstanding, Range of Exercise Prices, Minimum (in dollars per share)					$ 14.10	$ 20.29	$ 26.69
OSO units Outstanding, Range of Exercise Prices, Maximum (in dollars per share)					$ 16.99	$ 24.30	$ 36.60
OSO units Outstanding, Number Outstanding (in shares)	2,148,865				227,733	1,030,279	890,853		26,665			26,665
OSO units Outstanding, Average Remaining Contractual Term	1 year 5 months 15 days	1 year 8 months 23 days	1 year 6 months 11 days	1 year 8 months 23 days
OSO units Outstanding, Weighted Average Initial Strike Price (in dollars per share)	$ 23.99	$ 23.40	$ 20.51	$ 22.05				$ 10.79	$ 14.43	$ 12.18	$ 10.82
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(107,228)	(67,299)	(29,469)					(167,395)	(35,659)	(533,717)
OSO units Outstanding, Weighted Average Remaining Life (in years)					0 years 6 months 11 days	1 year 8 months 7 days	1 year 5 months 5 days		0 years 11 months 16 days			0 years 11 months 16 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	$ 32	$ 7	$ 2						$ 0
OSO units Outstanding, Weighted Average Initial Strike Price (in dollars per share)					$ 15.90	$ 21.92	$ 28.46		$ 14.43			$ 14.43
OSO units Exercisable, Number Exercisable (in shares)	0				0	0	0
OSO units Exercisable, Weighted Average Initial Strike Price (in dollars per share)	$ 0.00				$ 0.00	$ 0.00	$ 0.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	271,883	72,335	96,174							2,149
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price										$ 14.39
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	90,879	0	0