Derivatives - Additional Information (Detail) - USD ($)	3 Months Ended
Sep. 30, 2017	Jun. 30, 2017
Derivative [Line Items]
Maximum length of time hedged in cash flow hedge	3 years
Minimum required liquidity under certain counterparty agreements	$ 1,000,000,000
Minimum liquidity for the period as defined by certain counterparty agreements	1,000,000,000
Estimated derivative net gains (losses) included in AOCI that will be reclassified into earnings within 12 months	$ 29,000,000
Senior Unsecured Obligations
Derivative [Line Items]
Debt instrument credit rating	AAA
Derivatives Sold \| Foreign Exchange Contracts \| Non-designated Hedge Derivatives
Derivative [Line Items]
Notional amounts	$ 8,200,000,000	$ 10,600,000,000
Derivatives Sold \| Equity Contracts
Derivative [Line Items]
Notional amounts	2,600,000,000	2,400,000,000
Derivatives Sold \| Equity Contracts \| Designated Hedge Derivatives
Derivative [Line Items]
Notional amounts	1,800,000,000	1,800,000,000
Derivatives Sold \| Interest Rate Contracts \| Non-designated Hedge Derivatives
Derivative [Line Items]
Notional amounts	364,000,000	352,000,000
Derivatives Sold \| Credit Contracts \| Non-designated Hedge Derivatives
Derivative [Line Items]
Notional amounts	49,000,000	63,000,000
Derivatives Sold \| Cash flow hedging \| Foreign Exchange Contracts
Derivative [Line Items]
Notional amounts	8,900,000,000	8,900,000,000
Derivatives Sold \| Fair value hedging \| Foreign Exchange Contracts
Derivative [Line Items]
Notional amounts	5,000,000,000	5,100,000,000
Derivatives Purchased \| Foreign Exchange Contracts \| Non-designated Hedge Derivatives
Derivative [Line Items]
Notional amounts	11,000,000,000	8,800,000,000
Derivatives Purchased \| Equity Contracts
Derivative [Line Items]
Notional amounts	1,600,000,000	1,900,000,000
Derivatives Purchased \| Equity Contracts \| Designated Hedge Derivatives
Derivative [Line Items]
Notional amounts	1,600,000,000	1,600,000,000
Derivatives Purchased \| Interest Rate Contracts \| Non-designated Hedge Derivatives
Derivative [Line Items]
Notional amounts	528,000,000	233,000,000
Derivatives Purchased \| Mortgage-backed securities \| Non-designated Hedge Derivatives
Derivative [Line Items]
Notional amounts	553,000,000	567,000,000
Derivatives Purchased \| Credit Contracts \| Non-designated Hedge Derivatives
Derivative [Line Items]
Notional amounts	$ 252,000,000	$ 267,000,000

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

The minimum liquidity for the period as required by certain of our counterparty agreements for derivative instruments.

+ References

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- Definition

The minimum liquidity required by certain of our counterparty agreements for derivative instruments.

+ References

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- Definition

Description of the credit rating indicative of likelihood of repayment of the debt instrument given by a credit rating agency (for example, Standard and Poor's, Moody's, Fitch).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The estimated net amount of unrealized gains or losses on foreign currency cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

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- Definition

Maximum period of time the entity is hedging its exposure to variability in future cash flows for forecasted transactions, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Excludes forecasted transactions related to payment of variable interest on existing financial instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

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