Afilliate Equity - Schedule of the Effect of Changes in the Company's Ownership Interest in its Affiliates on the Controlling Interest's Equity (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Affiliate Equity [Abstract]
Net income (controlling interest)	$ 150.2	$ 110.2	$ 108.3	$ 104.0	$ 147.5	$ 107.7	$ 127.6	$ 126.7	$ 472.8	$ 509.5	$ 433.9
Increase in controlling interest paid-in capital from purchases and sales of Affiliate equity issuances									1.6	0.9	4.1
Decrease in controlling interest paid-in capital related to Affiliate equity repurchases									(38.0)	(87.6)	(33.2)
Net income attributable to controlling interest and transfers (to) or from Non-controlling interests									$ 436.4	$ 422.8	$ 404.8