Fair value of the assets less the liabilities of a derivative or group of derivatives.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13495-108611

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

Derivative Counterparties (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivative Counterparties Fair Value [Line Items]
Derivative, Fair Value, Net	$ 225	$ (174)
Wells Fargo Bank NA [Member]
Derivative Counterparties Fair Value [Line Items]
Credit Risk Derivative Assets At Fair Value	32
J.P. Morgan Chase Bank [Member]
Derivative Counterparties Fair Value [Line Items]
Credit Risk Derivative Assets At Fair Value	32
Citibank, N.A. [Member]
Derivative Counterparties Fair Value [Line Items]
Credit Risk Derivative Assets At Fair Value	24
ING Bank [Member]
Derivative Counterparties Fair Value [Line Items]
Credit Risk Derivative Assets At Fair Value	22
Societe Generale [Member]
Derivative Counterparties Fair Value [Line Items]
Credit Risk Derivative Assets At Fair Value	$ 20