Employee Benefit Arrangements - Fair Value of Plan Assets (Details)	12 Months Ended
	Dec. 31, 2024 USD ($) fund_asset	Dec. 31, 2023 USD ($) fund_asset	Dec. 31, 2022 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 1,773,000,000	$ 1,831,000,000
Redemption of investor's units, period of required notice	60 days
Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value	$ 0	0
U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value	0	0
U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value	0	0
Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value	0	0
Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	120,000,000	161,000,000
Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,384,000,000	1,360,000,000
Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	92,000,000	85,000,000
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,773,000,000	1,831,000,000	$ 1,770,000,000
Net, total pension assets, net asset value	177,000,000	225,000,000
Projected benefit obligation	1,912,000,000	1,999,000,000	$ 1,943,000,000
Accrued benefit cost	(331,000,000)	(350,000,000)
Prepaid benefit cost	192,000,000	182,000,000
Pension Plan | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,521,000,000	1,544,000,000
Net, total pension assets, net asset value	19,000,000	21,000,000
Pension Plan | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	18,000,000	9,000,000
Pension Plan | Hedge Funds, Equity
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	19,000,000
Net, total pension assets, net asset value	19,000,000	21,000,000
Pension Plan | U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	82,000,000	128,000,000
Pension Plan | U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,184,000,000	1,196,000,000
Pension Plan | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	152,000,000	151,000,000
Net, total pension assets, net asset value	$ 58,000,000	$ 68,000,000
Pension Plan | International Commingled Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of assets In fund | fund_asset	2	2
Pension Plan | International Commingled Funds | Baillie Gifford Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 26,000,000	$ 25,000,000
Unfunded commitments	0
Pension Plan | International Commingled Funds | Silchester
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 26,000,000	33,000,000
Number of business days prior to month-end clients must submit redemption request	6 days
Unfunded commitments	$ 0
Pension Plan | Other investments, including securities pledged
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	100,000,000	136,000,000
Net, total pension assets, net asset value	100,000,000	136,000,000
Pension Plan | Real estate | UBS Trumbull Property Fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 52,000,000	61,000,000
Real return performance objective, rate of return	5.00%
Pension Plan | Real estate | UBS Trumbull Property Fund | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Real return performance objective, rate of return, determination period	3 years
Pension Plan | Real estate | UBS Trumbull Property Fund | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Real return performance objective, rate of return, determination period	5 years
Pension Plan | Limited partnerships | Magnitude Institutional, Ltd.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 48,000,000	75,000,000
Pension Plan | Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	218,000,000	190,000,000
Pension Plan | Hedge Funds, Equity Long (Short)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value		21,000,000
Pension Plan | Level 1 | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	103,000,000	146,000,000
Pension Plan | Level 1 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	11,000,000	8,000,000
Pension Plan | Level 1 | Hedge Funds, Equity
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 1 | U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	82,000,000	128,000,000
Pension Plan | Level 1 | U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	10,000,000	10,000,000
Pension Plan | Level 1 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	17,000,000	15,000,000
Pension Plan | Level 1 | Other investments, including securities pledged
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 1 | Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,307,000,000	1,292,000,000
Pension Plan | Level 2 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	7,000,000	1,000,000
Pension Plan | Level 2 | Hedge Funds, Equity
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,102,000,000	1,121,000,000
Pension Plan | Level 2 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	77,000,000	68,000,000
Pension Plan | Level 2 | Other investments, including securities pledged
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	198,000,000	170,000,000
Pension Plan | Level 3 | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	92,000,000	85,000,000
Pension Plan | Level 3 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Hedge Funds, Equity
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	72,000,000	65,000,000
Pension Plan | Level 3 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Other investments, including securities pledged
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	20,000,000	20,000,000
Nonqualified pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Projected benefit obligation	331,000,000	350,000,000
Accumulated benefit obligation	$ 328,000,000	$ 348,000,000