Fair Value - Separate Accounts Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Dec. 31, 2023
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	$ 1,934	$ 3,311
Separate accounts liabilities	1,934	3,311	$ 3,334	$ 3,250
Recurring
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,891	3,499
Recurring | Other Receivables
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	43
Recurring | Other Payables
Fair Value, Separate Account Investment [Line Items]
Separate accounts liabilities		188
Recurring | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	160	165
Recurring | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	394	856
Recurring | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,337	2,478
Recurring | Level 1
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	36	187
Recurring | Level 1 | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	5	1
Recurring | Level 1 | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	31	186
Recurring | Level 1 | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Recurring | Level 2
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,854	3,311
Recurring | Level 2 | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	155	164
Recurring | Level 2 | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	362	669
Recurring | Level 2 | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1,337	2,478
Recurring | Level 3
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1	1
Recurring | Level 3 | Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	0	0
Recurring | Level 3 | Debt securities
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	1	1
Recurring | Level 3 | Common/collective trusts
Fair Value, Separate Account Investment [Line Items]
Separate accounts assets	$ 0	$ 0