Contingencies, Commitments and Guarantees (Contingencies - Narrative) (Details)	Dec. 31, 2017 USD ($)
Minimum
Loss Contingencies
Aggregate reasonably possible losses in excess of amounts accrued for loss contingency matters as to which an estimate can be made	$ 0
Maximum
Loss Contingencies
Aggregate reasonably possible losses in excess of amounts accrued for loss contingency matters as to which an estimate can be made	$ 10,000,000

The difference between the maximum amount of estimated loss and the amount recorded 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 05
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6395354&loc=d3e12631-108344

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