Investment Securities (Narrative) (Detail) $ in Billions	Jun. 30, 2017 USD ($) securities	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Pledged Securities, carrying value \| $	$ 1.5	$ 1.4	$ 1.4
Number of securities by a single non-goverment sponsored issuer exceeding 10% of shareholders' equity \| securities	0

The fair value of available-for-sale securities that serve as collateral for borrowings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

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