Fair value measurements - Reconciliation of Investments Measured at Fair Value using Level 3 Inputs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Other long-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 63.7	$ 87.0	$ 82.9	$ 86.6
Transfers in to (out of) Level 3	0.0	0.0	0.0	0.0
Purchases	0.0	0.0	0.0	0.0
Sales & Settlements	0.0	0.0	(22.7)	0.0
Realized and Unrealized Gains (Losses)	(6.2)	0.0	(2.7)	0.4
Ending balance	57.5	87.0	57.5	87.0
Net derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(31.7)	21.7	5.4	(13.4)
Transfers in to (out of) Level 3	0.0	0.0	0.0	0.0
Purchases	0.0	0.0	0.0	0.0
Sales & Settlements	0.0	0.0	(1.3)	5.4
Realized and Unrealized Gains (Losses)	8.8	(14.9)	(27.0)	14.8
Ending balance	$ (22.9)	$ 6.8	$ (22.9)	$ 6.8

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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