Deposits Deposits (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deposits [Abstract]
Domestic certificates of deposit of $250,000 or more	$ 462	$ 882
Foreign office time deposits in denominations of $250,000 or more	$ 15	$ 19

Amount of interest-bearing time deposits in foreign banking offices. Time deposits bear interest for a fixed, stated period of time and include certificate of deposits and individual retirement accounts.

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 210.9-03.12)
-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 942
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(a))
-URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537907-122884

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