Variable Interest Entities - Unconsolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	$ 305,046.7	$ 290,867.0
Money Market Funds
Total assets of unconsolidated money market mutual funds	3,800.0	4,200.0
Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Carrying value used if distributions received are in excess of investment	0.0
Corporate debt securities | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	364.9	111.8
Maximum exposure to loss	369.8	127.2
Residential mortgage-backed pass-through securities | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,061.1	2,228.7
Maximum exposure to loss	3,199.7	2,420.6
Residential mortgage-backed pass-through securities | Trading | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	10.4	5.4
Maximum exposure to loss	10.4	5.4
Commercial mortgage-backed securities | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	4,775.5	4,864.6
Maximum exposure to loss	5,428.6	5,572.2
Commercial mortgage-backed securities | Trading | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	53.1	83.4
Maximum exposure to loss	53.1	83.4
Collateralized debt obligations | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	5,403.7	4,566.4
Maximum exposure to loss	5,465.4	4,820.0
Collateralized debt obligations | Trading | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	2.0	5.7
Maximum exposure to loss	2.0	5.7
Other debt obligations | Available-for-sale | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	7,902.2	6,507.6
Maximum exposure to loss	9,002.9	7,566.2
Other debt obligations | Trading | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	228.4	80.0
Maximum exposure to loss	228.4	80.0
Equity securities | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	110.4	99.8
Maximum exposure to loss	110.4	99.8
Other investments: Other limited partnership and fund interests | Variable Interest Entity
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	2,091.7	1,473.5
Maximum exposure to loss	3,785.9	2,434.9
Fully secured debt of international real estate funds with recourse to the investment manager, included in maximum loss exposure	$ 251.9	$ 144.3