Investment Securities (Detail) $ in Billions	Sep. 30, 2016 USD ($) Security	Dec. 31, 2015 USD ($) Security
Investments, Debt and Equity Securities [Abstract]
Carrying value of pledged securities \| $	$ 1.3	$ 1.4
Number of debt securities held \| Security	73	252
Unrealized losses on debt securities (percent of amortized cost)	0.55%	1.10%

The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities.

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=66008989&loc=d3e5086-111524

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