Affiliate Equity - Schedule of Changes in the Company's Interest in its Affiliates on the Controlling Interest's Equity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Affiliate Equity [Abstract]
Net income (controlling interest)	$ 107.4	$ 128.7	$ 212.0	$ 256.7
Increase in controlling interest paid-in capital from purchases and sales of Affiliate equity issuances	(2.5)	0.5	(3.4)	1.0
Decrease in controlling interest paid-in capital related to Affiliate equity repurchases	(3.8)	(29.1)	(21.3)	(32.6)
Net income attributable to controlling interest and transfers (to) or from Non-controlling interests	$ 101.1	$ 100.1	$ 187.3	$ 225.1