Long-term Incentive Compensation Plans (Details) (USD $)	1 Months Ended		3 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Long-term Incentive Compensation Plans [Abstract]
Holding units purchased in period (in units)			1,000,000	4,500,000
Dollar amount paid for holding units acquired			$ 19,600,000	$ 66,000,000
Open-market purchases of holding units (in units)			800,000	4,300,000
Dollar amount paid for open-market purchases of holding units			16,000,000	63,200,000
Restricted holding unit awards to employees (in units)	6,500,000	8,700,000	6,600,000	9,100,000
Unallocated holding units remaining in the consolidated rabbi trust (in holding units)			12,500,000
Units issued upon options exercised (in units)			392,528
Proceeds from stock options exercised			$ 6,642,000	$ 0