Contingencies - Narrative (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Estimate of possible loss	$ 15,000,000
Unrecognized tax benefits	83,000,000	$ 94,000,000
Minimum
Loss Contingencies [Line Items]
Estimate of possible loss	0
Maximum
Loss Contingencies [Line Items]
Estimate of possible loss	30,000,000
Legal Reserve \| Invoicing Matter
Loss Contingencies [Line Items]
Estimate of possible loss	$ 360,000,000

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349

Name:	us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant