Income Taxes - Change in unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 7.0	$ 20.7	$ 56.9
Additions for tax positions related to the current year	0.0	0.0	0.0
Additions for tax positions of prior years	3.0	4.5	1.0
Reductions for tax positions of prior years	(0.3)	0.0	(25.8)
Settlements	(1.5)	(17.2)	(7.1)
Expiration of statute of limitations	(0.1)	(1.0)	(4.3)
Ending balance	$ 8.1	$ 7.0	$ 20.7

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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Amount of increase 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 lapses of applicable statutes of limitations.

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