Long-term Incentive Compensation Plans (Details) (USD $)	1 Months Ended		3 Months Ended
	Jul. 31, 2013	Jan. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Long-term Incentive Compensation Plans [Abstract]
Holding units purchased in period (in units)			200,000	1,000,000
Dollar amount paid for holding units acquired			$ 3,700,000	$ 19,600,000
Open-market purchases of holding units (in units)				800,000
Dollar amount paid for open-market purchases of holding units				16,000,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted holding unit awards to employees (in units)		6,500,000
Decrease in units outstanding (in units)	13,100,000
Units issued upon options exercised (in units)			273,084
Proceeds from stock options exercised			$ 4,656,000	$ 6,642,000
Employees and Eligible Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted holding unit awards to employees (in units)			200,000	6,600,000