Fair Value Measurements - Fair Values of Separate Account Assets (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	$ 569	$ 578
Non-guaranteed separate accounts	6,181	6,172
Subtotal	6,750	6,750
Non-guaranteed separate accounts priced at NAV as a practical expedient	666	680
Separate account assets	7,416	7,430
Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-guaranteed separate accounts	4,000	4,000
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	230	226
Non-guaranteed separate accounts	158	158
Subtotal	388	384
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	339	352
Non-guaranteed separate accounts	5,794	5,797
Subtotal	6,133	6,149
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	0	0
Non-guaranteed separate accounts	229	217
Subtotal	229	217
Significant Unobservable Inputs (Level 3) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-guaranteed separate accounts	$ 200	$ 200