Variable Interest Entities - Consolidated VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 246,903.9	$ 276,087.8
Total liabilities	233,691.6	261,137.1
Redeemable noncontrolling interest	239.7	264.9	$ 537.7	$ 391.2
Aggregate consolidated variable interest entities
Carrying amounts of consolidated VIE assets and liabilities
Total assets	32,331.6	40,802.1
Total liabilities	31,326.0	39,713.7
Redeemable noncontrolling interest	187.6	215.4
Grantor trust
Carrying amounts of consolidated VIE assets and liabilities
Total assets	35.1	99.9
Total liabilities	34.7	98.6
Mandatory retirement savings funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	31,535.3	39,891.1
Total liabilities	31,256.1	39,524.9
Real estate VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	421.5	479.7
Total liabilities	26.9	88.0
Sponsored investment funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	339.7	331.4
Total liabilities	8.3	2.2
Redeemable noncontrolling interest	$ 187.6	$ 215.4