Litigation and Regulatory Matters - Additional Information (Details) CAD in Millions	1 Months Ended	6 Months Ended
Jun. 30, 2017 USD ($)	Jun. 30, 2017 CAD
Loss Contingencies [Line Items]
Estimate of loss	$ 350,000,000
Canada FX Matters
Loss Contingencies [Line Items]
Litigation settlement \| CAD		CAD 15.5
ISDAFix
Loss Contingencies [Line Items]
Litigation settlement	$ 14,000,000

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