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Stock-Based Compensation - Grants of stock options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Stock-Based Compensation
Stock-based compensation	$ 6	$ 6	$ 11	$ 8
Series C common stock
Stock-Based Compensation
Options granted			181
Series B common stock
Stock-Based Compensation
Options granted			0
Series A common stock
Stock-Based Compensation
Options granted			0
Employee Stock Option
Stock-Based Compensation
Dividend rate			0.00%
Subsidiary employees \| Employee Stock Option \| Series C common stock
Stock-Based Compensation
Options granted			181
Vesting period			5 years
Weighted average GDFV			$ 26.4