Income Taxes Income Taxes - Valuation Allowance (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($)
Minimum [Member]
Valuation Allowance [Line Items]
Income Tax Reconciliation, Valuation Allowance Release	$ 50
Maximum [Member]
Valuation Allowance [Line Items]
Income Tax Reconciliation, Valuation Allowance Release	$ 60

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration