Investments - Schedule of Total Gains and Losses on Equity Securities (Detail) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Schedule of Investments [Abstract]
Total gains recognized on equity securities	$ 1	$ 15
Unrealized gains recognized on equity securities held at end of period	$ 1	$ 15

Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714

Name:	us-gaap_EquitySecuritiesFvNiGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration