Variable Interest Entities - Consolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 296,627.7	$ 276,087.8
Total liabilities	279,754.8	261,137.1
Redeemable noncontrolling interest	255.6	264.9	$ 391.2	$ 101.3
Aggregate consolidated variable interest entities
Carrying amounts of consolidated VIE assets and liabilities
Total assets	43,233.5	40,802.1
Total liabilities	41,552.4	39,713.7
Redeemable noncontrolling interest	226.8	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	41,995.2	39,891.1
Total liabilities	41,527.9	39,524.9
Real estate VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	499.0	479.7
Total liabilities	21.3	88.0
Sponsored investment funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	419.5	331.4
Total liabilities	3.2	2.2
Redeemable noncontrolling interest	226.8	$ 215.4
Residential mortgage loans
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 319.8