Net Recognized Gains (Losses) on Debt Investments (Detail) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Schedule Of Gain Loss On Investments Including Marketable Securities And Investments Held At Cost Income Statement Reported Amounts Summary [Line Items]
Realized gains from sales of available-for-sale securities	$ 7	$ 13
Realized losses from sales of available-for-sale securities	(85)	(80)
Total	243	573
Debt Securities
Schedule Of Gain Loss On Investments Including Marketable Securities And Investments Held At Cost Income Statement Reported Amounts Summary [Line Items]
Other-than-temporary impairments of investments	0	(1)
Total	$ (78)	$ (68)

Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of realized and unrealized gain (loss) on investment.

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Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
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