Separate Account Balances - Separate Account Asset (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Separate Account Assets
Total separate account assets per consolidated statements of financial position	$ 162,000.8	$ 155,375.1
Fixed maturities | Fixed maturities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	37,192.0	34,805.5
Fixed maturities | U.S. government and agencies
Separate Account Assets
Total separate account assets per consolidated statements of financial position	7,916.9	7,339.6
Fixed maturities | Non-U.S. governments
Separate Account Assets
Total separate account assets per consolidated statements of financial position	8,956.1	8,424.3
Fixed maturities | States and political subdivisions
Separate Account Assets
Total separate account assets per consolidated statements of financial position	225.9	211.7
Fixed maturities | Corporate debt securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	15,538.1	14,429.7
Fixed maturities | Residential mortgage-backed pass-through securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	3,994.7	3,894.5
Fixed maturities | Commercial mortgage-backed securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	199.5	206.2
Fixed maturities | Other debt obligations
Separate Account Assets
Total separate account assets per consolidated statements of financial position	360.8	299.5
Equity securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	109,562.8	105,053.3
Real estate
Separate Account Assets
Total separate account assets per consolidated statements of financial position	604.0	610.6
Other investments
Separate Account Assets
Total separate account assets per consolidated statements of financial position	9,887.0	10,278.6
Cash and cash equivalents
Separate Account Assets
Total separate account assets per consolidated statements of financial position	3,639.9	3,583.8
Other assets
Separate Account Assets
Total separate account assets per consolidated statements of financial position	$ 1,115.1	$ 1,043.3