Short-term Funding Short-term Funding (Details Textuals) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Short-term Debt [Abstract]
Collateral for repurchase agreements	$ 325

Carrying value of securities purchased under agreements to resell and deposits paid for securities borrowed.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.3)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(2))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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