Stock-Based Compensation (Details) 4 (USD $)
3 Months Ended
Mar. 31, 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) $ 44.49
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 292,984
Number of restricted units outstanding 775,207
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 847,220
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) $ 44.84
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) $ 47.31
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 144,607
Number of restricted units outstanding 316,990
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 67,064
Number of restricted units outstanding 73,378
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) $ 44.71
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