Taxation (Uncertain tax positions) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Unrecognized Tax Benefits
Balance beginning of year	$ 101.6	$ 43.7
Increases as a result of positions taken in prior years	1.1	70.4
Increases as a result of positions taken during the current year	0.0	10.1
Decreases as a result of positions taken in prior years	(60.7)	(22.6)
Settlements	(1.8)	0.0
Unrecognized tax benefits	$ 40.2	$ 101.6

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 unrecognized tax benefits.

+ References

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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