Separate Account Balances - Separate Account Asset (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Separate Account Assets
Total separate account assets per consolidated statements of financial position	$ 202,396.0	$ 193,622.6
Fixed maturities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	37,159.9	36,869.8
Fixed maturities \| U.S. government and agencies
Separate Account Assets
Total separate account assets per consolidated statements of financial position	10,446.7	10,027.9
Fixed maturities \| Non-U.S. governments
Separate Account Assets
Total separate account assets per consolidated statements of financial position	9,072.5	9,122.1
Fixed maturities \| States and political subdivisions
Separate Account Assets
Total separate account assets per consolidated statements of financial position	147.4	162.3
Fixed maturities \| Corporate debt securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	13,279.2	13,404.2
Fixed maturities \| Residential mortgage-backed pass-through securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	3,476.1	3,484.1
Fixed maturities \| Commercial mortgage-backed securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	292.7	261.2
Fixed maturities \| Other debt obligations
Separate Account Assets
Total separate account assets per consolidated statements of financial position	445.3	408.0
Equity securities
Separate Account Assets
Total separate account assets per consolidated statements of financial position	152,607.9	141,251.0
Real estate
Separate Account Assets
Total separate account assets per consolidated statements of financial position	445.0	445.9
Other investments
Separate Account Assets
Total separate account assets per consolidated statements of financial position	7,999.7	8,848.3
Cash and cash equivalents
Separate Account Assets
Total separate account assets per consolidated statements of financial position	3,272.1	5,135.4
Other assets
Separate Account Assets
Total separate account assets per consolidated statements of financial position	$ 911.4	$ 1,072.2