Stock-Based Compensation (Restricted Stock Units and PBRSU) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Compensation PBRSU percent of target	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures			581,265
Restricted Stock [Member]
Number of Shares
Outstanding, Beginning of Period	1,381,000
Granted	593,164		640,667
Vested	(450,000)
Forfeited	(7,000)
Outstanding, End of Period	1,517,000
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning Balance	17.50
Granted, Weighted Average Grant Date Fair Value	26.11
Vested, Weighted Average Grant Date Fair Value	17.21
Forfeited, Weighted Average Exercise Price	18.20
Weighted Average Grant Date Fair Value, Ending Balance	20.95
Restricted stock units, estimated grant date fair value	15.5		10.5
Award vesting period	3 years
Total unrecognized compensation cost related to unvested awards	25.5
Nonvested awards, weighted average remaining period (in years)	2.4
PBRSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.00%
Number of Shares
Outstanding, Beginning of Period	1,151,000
Granted	390,000		345,348
Vested	(157,000)
Forfeited	(23,000)
Outstanding, End of Period	1,361,000
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning Balance	17.21
Granted, Weighted Average Grant Date Fair Value	26.02
Vested, Weighted Average Grant Date Fair Value	18.18
Forfeited, Weighted Average Exercise Price	17.73
Weighted Average Grant Date Fair Value, Ending Balance	18.40
Restricted stock units, estimated grant date fair value	10.2		5.5
Total unrecognized compensation cost related to unvested awards	19.6
Nonvested awards, weighted average remaining period (in years)	2.1
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	0.35%	[1]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	30.59%	[2]
Share-based Compensation Arrangement, Fair Value, Average Shareholder Return [Abstract]	8.21%	[3]

[1] The risk-free interest rate for the periods within the contractual term of the options is based on the U.S. Treasury yield curve in effect at the time of the grant.

[2] The expected volatility and average total shareholder return is a measure of the amount by which a stock price has fluctuated or is expected to fluctuate based primarily on our and our peers' historical data.

[3] The expected life is the period of time, on average, that participants are expected to hold their options before exercise based primarily on our historical data.