Contractholder Funds - Changes in Policyholder Account Balances, Benefits and Protection (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2026	Dec. 31, 2025
Changes in policyholder account balances
Policyholder account balance, beginning of period	$ 30,318.1
Policyholder account balance, end of period	32,959.0	$ 30,318.1
Benefits and Protection \| Life Insurance \| Universal life
Changes in policyholder account balances
Policyholder account balance, beginning of period	6,867.5	6,953.7
Premiums and deposits	982.6	1,305.7
Policy charges	(664.4)	(886.0)
Surrenders, withdrawals and benefit payments	(698.5)	(587.7)
Net transfers from (to) separate account	(89.4)	(198.1)
Interest credited	218.0	304.2
Change in fair value of embedded derivative	14.4	17.3
Other	(37.5)	(41.6)
Policyholder account balance, end of period	6,592.7	6,867.5
Reinsurance impact	(2,902.4)	(3,045.1)
Policyholder account balance at end of period after reinsurance	$ 3,690.3	$ 3,822.4
Weighted-average crediting rate	4.19%	4.11%
Net amount at risk	$ 85,508.6	$ 86,094.5
Cash surrender value	$ 5,812.6	$ 6,045.7

Amount of reinsurance impact on policyholder account balances.

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Amount of decrease in liability for policyholder account balance from contract redemption, withdrawal of funds or benefit payments.

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Amount, after effect of reinsurance, of policyholder funds.

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Amount of cash to be paid to policyholder upon termination and surrender of long-duration contract issued by insurance entity.

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Net Increase or Decrease in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period.

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Amount of interest expense for allocation to policyholder account balance.

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Amount of increase (decrease) in liability for policyholder account balance from change, classified as other.

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Amount of guaranteed benefit in excess of current account balance of policyholder account balance.

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Amount of decrease in liability for policyholder account balance from policy charge.

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Amount of cash inflow to policyholder account balance from premium received.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted-average crediting rate for liability for policyholder account balance, calculated at a point in time.

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Amount due to policyholder. Includes, but is not limited to, unpaid policy dividend, retrospective refund, and undistributed earnings on participating business. Excludes future policy benefit and claim expense.

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Amount of transfer to (from) liability for policyholder account balance (to) from liability for separate account.

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