Investments - Schedule of Total Gains and Losses on Equity Securities (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Investments Schedule [Abstract]
Total (losses) gains recognized on equity securities	$ (44)	$ 2	$ (29)	$ (17)
Less: Losses recognized on equity securities sold or impaired	0	(30)	0	(24)
Unrealized (losses) gains recognized on equity securities held at end of period	$ (44)	$ 32	$ (29)	$ 7