Fair Value Measurements - Fair Value of Investment Assets (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	$ 121	$ 181
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Amortized Cost	124	184
Level 1 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	0	80
Level 1 | Fair Value | Fixed Income Mutual Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	0	80
Level 1 | Fair Value | Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	0	0
Level 1 | Fair Value | Government Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	0	0
Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	121	101
Level 2 | Fair Value | Fixed Income Mutual Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	0	0
Level 2 | Fair Value | Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	72	60
Level 2 | Fair Value | Government Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	49	41
Total | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	121	181
Total | Fair Value | Fixed Income Mutual Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	0	80
Total | Fair Value | Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	72	60
Total | Fair Value | Government Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Investments at Fair Value	$ 49	$ 41