Separate Account Balances - Separate Account Asset (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Separate Account Assets
Total separate account assets per consolidated statements of financial position	$ 155,478.2	$ 155,375.1
Fixed maturities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	33,257.1	34,805.5
Fixed maturities | U.S. government and agencies
Separate Account Assets
Total separate account assets per consolidated statements of financial position	8,156.2	7,339.6
Fixed maturities | Non-U.S. governments
Separate Account Assets
Total separate account assets per consolidated statements of financial position	7,618.1	8,424.3
Fixed maturities | States and political subdivisions
Separate Account Assets
Total separate account assets per consolidated statements of financial position	198.5	211.7
Fixed maturities | Corporate debt securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	12,808.7	14,429.7
Fixed maturities | Residential mortgage-backed pass-through securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	3,776.9	3,894.5
Fixed maturities | Commercial mortgage-backed securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	213.1	206.2
Fixed maturities | Other debt obligations
Separate Account Assets
Total separate account assets per consolidated statements of financial position	485.6	299.5
Equity securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	108,349.0	105,053.3
Real estate
Separate Account Assets
Total separate account assets per consolidated statements of financial position	497.0	610.6
Other investments
Separate Account Assets
Total separate account assets per consolidated statements of financial position	8,688.9	10,278.6
Cash and cash equivalents
Separate Account Assets
Total separate account assets per consolidated statements of financial position	3,757.2	3,583.8
Other assets
Separate Account Assets
Total separate account assets per consolidated statements of financial position	$ 929.0	$ 1,043.3