Fair Value Measurements Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
US Government Securities, at Carrying Value	$ 0	$ 0
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	16	16
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Debt Securities, Available-for-sale	16	16
Fair Value, Inputs, Level 1, Level 2, and Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	474	730
US Government Securities, at Carrying Value	16	16
US Government Securities, at Carrying Value	42	22
Assets, Fair Value Disclosure	532	768
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	474	730
US Government Securities, at Carrying Value	16	16
US Government Securities, at Carrying Value	42	22
Assets, Fair Value Disclosure	532	768
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
US Government Securities, at Carrying Value	0	0
Assets, Fair Value Disclosure	$ 0	$ 0