Commitments, Contingencies and Guarantees - Commitments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Commitments to extend credit	$ 27,755,976	$ 27,743,387
Financial Standby Letter of Credit
Guarantor Obligations [Line Items]
Standby and commercial letters of credit	$ 1,429,550	$ 1,446,903

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

Name:	us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant