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Debt (Loans) (Details) ¥ in Millions, SFr in Millions, $ in Millions	3 Months Ended				12 Months Ended
	Mar. 31, 2026 USD ($)	Dec. 31, 2025 CNY (¥)	Dec. 31, 2025 CHF (SFr)	Sep. 30, 2025 CNY (¥)	Mar. 31, 2026 USD ($)	Mar. 31, 2025 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2026 CNY (¥)	Mar. 31, 2026 CHF (SFr)	Mar. 31, 2025 CNY (¥)	Mar. 31, 2025 CHF (SFr)
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 6,572				$ 6,572	$ 5,790
Long-term debt, principal	6,619				6,619	5,832
Proceeds from issuance of long-term and short-term borrowings					1,779	2,268	$ 749
China Loan, Due September 2027
Debt Instrument [Line Items]
Long-term debt, carrying value	14				14	13
Long-term debt, principal	14				14	13		¥ 100		¥ 100
Proceeds from issuance of long-term and short-term borrowings \| ¥				¥ 100
Interest rates				0.55%
China Loan, due November 2027
Debt Instrument [Line Items]
Long-term debt, carrying value	22				22	21
Long-term debt, principal	22				22	21		149		150
Proceeds from issuance of long-term and short-term borrowings \| ¥		¥ 150
Interest rates		0.40%	0.40%
China Loan, due December 2027
Debt Instrument [Line Items]
Long-term debt, carrying value	22				22	21
Long-term debt, principal	22				22	21		149		¥ 150
Proceeds from issuance of long-term and short-term borrowings \| ¥		¥ 150
Interest rates		0.50%	0.50%
Sierre Loan, due October 2027
Debt Instrument [Line Items]
Long-term debt, carrying value	125				125	113
Long-term debt, principal	125				125	113			SFr 100		SFr 100
Proceeds from issuance of long-term and short-term borrowings \| SFr			SFr 100
Interest rates		0.50%	0.50%
China Loan, due January 2029
Debt Instrument [Line Items]
Long-term debt, carrying value	26				26	0
Long-term debt, principal	26				$ 26	$ 0		¥ 180
Proceeds from issuance of long-term and short-term borrowings	$ 180
Interest rates	0.60%				0.60%			0.60%	0.60%
China Bank Loans, due August 2027
Debt Instrument [Line Items]
Long-term debt, carrying value \| ¥								¥ 200
China \| Maximum
Debt Instrument [Line Items]
Unsecured debt \| ¥								¥ 500