Long-term Incentive Compensation Plans (Details) - USD ($) $ in Thousands, shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Holding units purchased in period	3.0	0.1	3.8	0.2
Dollar amount paid for holding units acquired	$ 82,100	$ 1,300	$ 103,400	$ 5,400
Open-market purchases of holding units	3.0		3.7
Dollar amount paid for open-market purchases of holding units	$ 82,100		$ 101,100
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units issued upon options exercised (in units)			0.5	0.8
Proceeds from stock options exercised			$ 8,979	$ 12,849
Employees and Eligible Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted holding unit awards to employees (in units)			0.3	0.8