Long-Term Incentive Compensation (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Long-term incentive compensation expense
Long-term incentive awards granted			$ 55.8
Vesting period			4 years
Long-term incentive compensation expense related to mark-to-market adjustments	15.8	16.2	45.3	51.0
Restricted stock awards
Long-term incentive compensation expense
Long-term incentive awards granted			33.4
Number of shares granted (in shares)			3.5
Weighted average price per share (in dollars per share)			$ 9.55
Mutual fund share awards
Long-term incentive compensation expense
Long-term incentive awards granted			22.2
Stock Options
Long-term incentive compensation expense
Long-term incentive awards granted			0.2
Deferred compensation plans
Long-term incentive compensation expense
Long-term incentive compensation expense related to mark-to-market adjustments	$ 2.4	$ 1.7	$ 5.7	$ 4.3