Variable Interest Entities - Consolidated VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 42,582.2	$ 38,922.8
Total liabilities	41,531.8	37,742.9
Grantor trust
Carrying amounts of consolidated VIE assets and liabilities
Total assets	98.6	95.0
Total liabilities	95.3	89.4
Commercial mortgage-backed securities VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	5.4	6.4
Mandatory retirement savings funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	41,743.8	37,915.7
Total liabilities	41,354.2	37,579.3
Real estate VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	397.0	379.2
Total liabilities	78.3	70.6
Sponsored investment funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	337.4	526.5
Total liabilities	4.0	3.6
Redeemable noncontrolling interest	$ 194.9	$ 325.7