Stock-Based Compensation (Details) 4 (USD $)
6 Months Ended
Jun. 30, 2014
Restricted Stock Units Performance Based [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Vesting period 3 years
LTIP Plan [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Weighted average grant date fair value of restricted units outstanding (per unit) $ 44.55
LTIP Plan [Member] | Restricted Stock Units Time Based [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of restricted units granted 300,899
Number of restricted units outstanding 757,020
LTIP Plan [Member] | Restricted Stock Units Performance Based [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of restricted units granted 392,388
Number of restricted units outstanding 830,880
LTIP Plan [Member] | Restricted Stock Units (RSUs) [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Weighted average grant date value of restricted units granted (per unit) $ 44.83
Assumed Plans [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Weighted average grant date fair value of restricted units outstanding (per unit) $ 46.83
Assumed Plans [Member] | Restricted Stock Units Time Based [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of restricted units granted 153,049
Number of restricted units outstanding 305,008
Assumed Plans [Member] | Restricted Stock Units Performance Based [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of restricted units granted 84,614
Number of restricted units outstanding 80,046
Assumed Plans [Member] | Restricted Stock Units (RSUs) [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Weighted average grant date value of restricted units granted (per unit) $ 44.44
Straight Line Vesting Basis [Member] | Restricted Stock Units Time Based [Member] | Minimum [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Vesting period 2 years
Straight Line Vesting Basis [Member] | Restricted Stock Units Time Based [Member] | Maximum [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Vesting period 4 years
Cliff Vesting [Member] | Restricted Stock Units Time Based [Member] | Minimum [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Vesting period 3 years
Cliff Vesting [Member] | Restricted Stock Units Time Based [Member] | Maximum [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Vesting period 4 years