Variable Interest Entities - Unconsolidated VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	$ 299,408.2	$ 290,578.3
Money Market Funds
Total assets of unconsolidated money market mutual funds	4,500.0	4,200.0
Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Carrying value used if distributions received are in excess of investment	0.0	0.0
Corporate debt securities | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	162.9	111.8
Maximum exposure to loss	174.8	127.2
Residential mortgage-backed pass-through securities | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	2,794.9	2,228.7
Maximum exposure to loss	2,951.5	2,420.6
Residential mortgage-backed pass-through securities | Trading | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	11.1	5.4
Maximum exposure to loss	11.1	5.4
Commercial mortgage-backed securities | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	4,927.8	4,864.6
Maximum exposure to loss	5,555.1	5,572.2
Commercial mortgage-backed securities | Trading | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	78.7	83.4
Maximum exposure to loss	78.7	83.4
Collateralized debt obligations | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	4,902.3	4,566.4
Maximum exposure to loss	5,136.6	4,820.0
Collateralized debt obligations | Trading | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	4.7	5.7
Maximum exposure to loss	4.7	5.7
Other debt obligations | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	6,906.7	6,507.6
Maximum exposure to loss	7,934.9	7,566.2
Other debt obligations | Trading | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	30.2	80.0
Maximum exposure to loss	30.2	80.0
Equity securities | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	110.2	99.8
Maximum exposure to loss	110.2	99.8
Other investments: Other limited partnership and fund interests | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	1,539.5	1,473.5
Maximum exposure to loss	2,614.6	2,434.9
Fully secured debt of international real estate funds with recourse to the investment manager, included in maximum loss exposure	$ 146.7	$ 144.3