Share-Based Compensation Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	May 29, 2013	Mar. 21, 2013	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 11,931,000	$ 21,482,000	$ 7,613,000
Shares authorized to be purchased	50,000,000	50,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	84,500				155,000	92,000
Trading Days		20 days
Employee Stock Purchase Plan [Abstract]
Compensation expense recognized	11,932,000	21,482,000	13,993,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	2,800,000
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	5,900,000
Recognization of share-based compensation expenses, weighted average period	1 year 11 months
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares exercised	(182,000)	(7,000)	(153,000)
Total intrinsic value of options exercised	9,600,000	300,000	5,700,000
Cash received from exercised options	6,400,000	300,000	3,400,000
Shares exercisable at period end		193,000
Shares exercised, weighted average exercise price		$ 36.04
97 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, contractual term	10 years
Award vesting period	3 years
07 Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, contractual term	10 years
Award vesting period	3 years
Minimal age when award becomes fully vested	60 years
Amended and restated employment agreement | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, contractual term			6 years
Award vesting period			3 years
Shares authorized to be purchased							180,000
Employee agreement | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Shares authorized to be purchased							130,000
Shares exercised	(180,000)		(130,000)
Shares granted (in dollars per share)	$ 35.19		$ 36.16
Shares exercised, minimum price	$ 85.00		$ 57.36
Shares exercised, maximum price	$ 91.33		$ 60.05
Omnibus Stock Incentive Plans, 2007 New LTIP [Member]
Employee Stock Purchase Plan [Abstract]
Compensation expense recognized	8,300,000	12,800,000
04 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years
Minimal age when award becomes fully vested	60 years
Previous employment agreement | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual interest rate				3.00%
Period before options become vested subsequent to termination				6 months
Churchill 2004 and 2007 Plan [Member] | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, vested	(346,000)	(316,000)	(221,000)
Shares held by Company subject to performance-based vesting criteria	341,000	673,000	379,000	419,000
Minimum | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognization of share-based compensation expenses, weighted average period	17 months
Employee Stock Purchase Plan [Member]
Employee Stock Purchase Plan [Abstract]
Number of hours required to be considered a full time employee	20 hours
Number of months per year that an employee needs to work to be considered full-time	5 months
Percentage of common stock purchase price that employee allowed to purchase at	85.00%
Maximum stock allowed to be purchased by employee in one year, value	25,000
Stock sold by company to employees	15,000
Compensation expense recognized	$ 400,000
Criteria One | Amended and restated employment agreement | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares issued to director	30,000	15,000		45,000
Consecutive trading days mimimum price per share must be met for options to vest				20 days
Criteria One | Previous employment agreement | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares issued to director		60,000		90,000
Consecutive trading days mimimum price per share must be met for options to vest				20 days
Criteria Two | Amended and restated employment agreement | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				6 years
Restricted shares required before shares become exercisable				81,250
Criteria Two | Previous employment agreement | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				5 years
Restricted shares required before shares become exercisable				65,000
Consecutive trading days mimimum price per share must be met for options to vest				10 days
Criteria Three | Previous employment agreement | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				5 years
Restricted shares required before shares become exercisable				65,000
Performance-Based Awards [Member] | Churchill 2004 and 2007 Plan [Member] | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, vested	(239,000)	(60,000)	(52,000)
Shares held by Company subject to performance-based vesting criteria	84,500	324,000	60,000	112,000