Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Changes in Unrecognized Tax Benefits
Beginning balance, Unrecognized tax benefits	$ 207.8	$ 219.0
Additions based on tax positions related to the current year	7.2	0.8
Additions for tax positions of prior years	20.2	0.8
Reductions for tax positions related to the current year	(3.3)	(12.6)
Reductions for tax positions of prior years	(1.1)	(0.2)
Settlements	(36.7)
Ending balance, Unrecognized tax benefits	194.1	207.8
Amount of unrecognized tax benefits that would reduce the effective income tax rate, if recognized	51.7
Accumulated pre-tax interest and penalties related to unrecognized tax benefits	$ 125.5	$ 142.4

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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Amount of unrecognized tax benefits.

+ References

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-Section 50
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Amount of decrease 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 decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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