Stock-based Compensation (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Feb. 20, 2014
Stock-based Compensation arrangements
Stock based compensation expense	$ 5,900,000	$ 3,200,000
Tax benefits realized for stock-based compensation	3,400,000	16,000,000
Supplemental Employee Incentive Plan IV
Stock-based Compensation arrangements
Stock based compensation expense	(100,000)	1,500,000
Assumptions:
Stock price volatility	31.30%
Risk free rate of return	0.70%
Annual salary increase rate	4.00%
Annual turnover rate	4.60%
Restricted Stock Awards
Stock-based Compensation arrangements
Granted (in shares)	2,400
Granted (in dollars per share)	$ 27.53
Annual forfeiture rate assumption (as a percent)	5.00%
Restricted Stock Units
Stock-based Compensation arrangements
Granted (in shares)	45,450
Granted (in dollars per share)	$ 27.76
Performance Share Awards | Minimum
Stock-based Compensation arrangements
Annual forfeiture rate assumption (as a percent)	0.00%
Performance Share Awards | Maximum
Stock-based Compensation arrangements
Annual forfeiture rate assumption (as a percent)	5.00%
Performance Share Awards Based on Internal Performance Metrics | Maximum
Stock-based Compensation arrangements
Right to receive additional shares (as a percent)	100.00%
Employee Performance Share Awards
Stock-based Compensation arrangements
Granted (in shares)	349,780
Granted (in dollars per share)	$ 27.71
Number of years over which performance criteria is to be met	3 years
Hybrid Performance Share Awards
Stock-based Compensation arrangements
Granted (in shares)	194,947
Granted (in dollars per share)	$ 27.71
Vesting rights	The 2015 awards vest 25% on each of the first and second anniversary dates and 50% on the third anniversary
Minimum operating cash flow for the year preceding the performance period	$ 100,000,000
Hybrid Performance Share Awards | Hybrid performance share awards, percentage vesting on each of the first and second anniversary
Stock-based Compensation arrangements
Award vesting rights, percentage	25.00%
Hybrid Performance Share Awards | Hybrid performance share awards, percentage vesting on the third anniversary
Stock-based Compensation arrangements
Award vesting rights, percentage	50.00%
Performance Shares Based on Market Conditions | Maximum
Stock-based Compensation arrangements
Right to receive shares (as a percent)	100.00%
Right to receive an additional award in cash (as a percent)	100.00%
TSR Performance Share Awards
Stock-based Compensation arrangements
Granted (in shares)	292,421
Performance period	3 years
Assumptions:
Fair value per performance share award (in dollars per share)			$ 19.29
Stock price volatility			32.30%
Risk free rate of return			1.00%
Expected dividend yield	0.30%		0.30%
Stock price volatility, minimum	29.30%
Stock price volatility, maximum	30.30%
Risk free rate of return, minimum	0.20%
Risk free rate of return, maximum	0.80%
Fair value per performance share award, minimum (in dollars per share)	$ 10.37
Fair value per performance share award, maximum(in dollars per share)	$ 14.21