Variable Interest Entities - Consolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 278,484.8		$ 276,087.8
Total liabilities	262,485.2		261,137.1
Redeemable noncontrolling interest	278.5	$ 272.7	264.9	$ 369.3	$ 304.5	$ 391.2
Aggregate consolidated variable interest entities
Carrying amounts of consolidated VIE assets and liabilities
Total assets	37,943.1		40,802.1
Total liabilities	36,696.7		39,713.7
Redeemable noncontrolling interest	210.5		215.4
Grantor trust
Carrying amounts of consolidated VIE assets and liabilities
Total assets			99.9
Total liabilities			98.6
Mandatory retirement savings funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	37,065.6		39,891.1
Total liabilities	36,663.4		39,524.9
Real estate VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	482.3		479.7
Total liabilities	28.0		88.0
Sponsored investment funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	395.2		331.4
Total liabilities	5.3		2.2
Redeemable noncontrolling interest	$ 210.5		$ 215.4