Contractholder Funds - Changes in Policyholder Account Balances (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2024	Dec. 31, 2023
Changes in policyholder account balances
Policyholder account balance, beginning of period	$ 25,322.2
Policyholder account balance, end of period	25,574.7	$ 25,322.2
Retirement and Income Solutions
Changes in policyholder account balances
Policyholder account balance, beginning of period	18,774.0
Policyholder account balance, end of period	19,031.5	18,774.0
Retirement and Income Solutions \| Workplace savings and retirement solutions
Changes in policyholder account balances
Policyholder account balance, beginning of period	12,721.5	12,154.7
Premiums and deposits	2,424.5	4,441.7
Policy charges	(18.4)	(31.6)
Surrenders, withdrawals and benefit payments	(1,901.3)	(4,356.6)
Net transfers from (to) separate account	(96.8)	264.8
Interest credited	182.0	280.2
Other	(17.6)	(31.7)
Policyholder account balance, end of period	$ 13,293.9	$ 12,721.5
Weighted-average crediting rate	3.00%	2.54%
Cash surrender value	$ 11,782.8	$ 11,211.9
Retirement and Income Solutions \| Individual variable annuities
Changes in policyholder account balances
Policyholder account balance, beginning of period	514.2	381.4
Premiums and deposits	540.0	586.7
Policy charges	(0.8)
Surrenders, withdrawals and benefit payments	(840.9)	(1,123.0)
Net transfers from (to) separate account	619.7	659.3
Interest credited	4.7	9.8
Other	1.1
Policyholder account balance, end of period	$ 838.0	$ 514.2
Weighted-average crediting rate	3.47%	3.22%
Cash surrender value	$ 859.0	$ 512.6
Retirement and Income Solutions \| Individual fixed deferred annuities
Changes in policyholder account balances
Policyholder account balance, beginning of period	5,538.3	7,228.3
Premiums and deposits	24.0	36.8
Surrenders, withdrawals and benefit payments	(732.5)	(1,888.4)
Interest credited	69.8	161.6
Policyholder account balance, end of period	$ 4,899.6	$ 5,538.3
Weighted-average crediting rate	2.99%	2.84%
Cash surrender value	$ 4,608.9	$ 5,434.4
Benefits and Protection \| Life Insurance \| Universal life
Changes in policyholder account balances
Policyholder account balance, beginning of period	6,910.4	6,947.9
Premiums and deposits	666.0	1,260.5
Policy charges	(437.1)	(858.1)
Surrenders, withdrawals and benefit payments	(323.4)	(483.6)
Net transfers from (to) separate account	(66.4)	(197.7)
Interest credited	147.4	242.1
Other	(0.7)	(0.7)
Policyholder account balance, end of period	6,896.2	6,910.4
Reinsurance impact	(3,312.1)	(3,396.8)
Policyholder account balance at end of period after reinsurance	$ 3,584.1	$ 3,513.6
Weighted-average crediting rate	4.13%	4.01%
Net amount at risk	$ 86,091.1	$ 86,671.0
Cash surrender value	$ 5,973.2	$ 5,953.0

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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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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