Related Party - Gilead Sciences, Inc. (Details) shares in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2026 USD ($) program member	Mar. 31, 2025 USD ($) shares	Dec. 31, 2023 USD ($) program	Dec. 31, 2021 USD ($) program	Dec. 31, 2020 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Related Party Transaction [Line Items]
Sale of stock, consideration received on transaction		$ 150.0
Number of programs, eligible to receive regulatory and commercial milestone payments \| program			4
Revenue recognized from amounts in deferred revenue at the beginning of the period	$ 17.0	28.0
Accounts payable, current	$ 39.0					$ 42.0
Gilead
Related Party Transaction [Line Items]
Sale of stock, consideration received on transaction		$ 15.0
Gilead
Related Party Transaction [Line Items]
Sale of stock, number of shares acquired in transaction (in shares) \| shares		1.4
Related Party
Related Party Transaction [Line Items]
Percentage of outstanding common stock held	25.00%
Accounts payable, current	$ 11.0					$ 24.0
Related Party \| Research and Development
Related Party Transaction [Line Items]
Reimbursement from related party for shared costs		$ (5.0)
Purchase Agreement \| Related Party
Related Party Transaction [Line Items]
Number of board members \| member	3
Gilead Collaboration Agreement
Related Party Transaction [Line Items]
Option payment upon completion of certain IND-enabling activities	$ 60.0
Option payment upon achievement of certain development milestones	$ 150.0
Gilead Collaboration Agreement \| Related Party
Related Party Transaction [Line Items]
Collaboration term for current and future clinical programs					10 years
Option continuation payment due upon second anniversary of agreement					$ 100.0
Option continuation payment due upon fourth anniversary of agreement					100.0		$ 100.0
Option continuation payment due upon sixth anniversary of agreement					100.0
Option continuation payment due upon eighth anniversary of agreement					100.0
Upfront cash payment					$ 175.0
Option fee per program for all other programs entering clinical development to exercise option				$ 150.0
Number of research programs \| program	2
Revenue recognized from amounts in deferred revenue at the beginning of the period	$ 15.0	$ 28.0
Gilead Collaboration Agreement \| Related Party \| Maximum
Related Party Transaction [Line Items]
Potential regulatory approval milestones payment receivable related to domvanalimab				$ 500.0
Amended Gilead Collaboration Agreement
Related Party Transaction [Line Items]
Number of exercise option to programs \| program				3
Option payments received				$ 725.0
Removal of option continuation payment under agreement				$ 100.0
Option payment upon achievement of certain development milestones			$ 150.0
Number of programs, eligible to receive regulatory and commercial milestone payments \| program			2
Amended Gilead Collaboration Agreement \| Related Party
Related Party Transaction [Line Items]
Upfront cash payment			$ 17.5
Number of research programs \| program			2
Option payment upon completion of certain IND-enabling activities			$ 45.0
Total upfront cash payment			35.0
Amended Gilead Collaboration Agreement \| Related Party \| Maximum
Related Party Transaction [Line Items]
Regulatory and commercial milestone payments received			$ 375.0

Arcus Biosciences, Inc. 10-Q