Redeemable Series A Preferred Stock - Narrative (Details) - USD ($)		12 Months Ended
	Jan. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016	Jan. 30, 2018
Temporary Equity [Line Items]
Preferred stock authorized (in shares)		2,500,000	2,500,000		5,000,000
Preferred stock par value (in usd per share)		$ 1.00	$ 1.00
Preferred stock issued (in shares)		700,000	700,000
Number of warrants issued (in shares)	1,625,000
Warrant exercise price (in usd per share)	$ 1.00
Issued preferred stock, warrants, and options proceeds, net of issuance costs	$ 631,000,000	$ 631,000,000	$ 0	$ 0
Transaction costs	19,000,000
Proceeds from issuance of preferred stock	515,400,000
Proceeds from issuance of warrants	103,100,000
Proceeds from issuance of options to purchase stock	12,500,000
Series A Preferred Stock
Temporary Equity [Line Items]
Preferred stock authorized (in shares)					2,500,000
Preferred stock par value (in usd per share)		$ 1.00			$ 1,000
Preferred stock issued, value	$ 650,000,000
Preferred stock issued (in shares)	650,000
Period for which preferred stock is non-callable	3 years
Dividend as percentage of accrued stated value	6.00%
Dividend, basis spread on variable rate	0.50%
Partial redemption limit, accrued stated value (not less than)	$ 50,000,000
Partial redemption limit, accrued stated value of preferred stock outstanding (not less than)	$ 100,000,000
Number of trading days preceding notice of conversion	30 days
Redemption during fourth or fifth year after issuance | Series A Preferred Stock
Temporary Equity [Line Items]
Redemption percentage	106.00%
Redemption during sixth year after issuance | Series A Preferred Stock
Temporary Equity [Line Items]
Redemption percentage	103.00%
Redemption after sixth year after issuance | Series A Preferred Stock
Temporary Equity [Line Items]
Redemption percentage	100.00%
Call Option
Temporary Equity [Line Items]
Options to purchase stock (in shares)	875,000
Options to purchase stock, exercise price (in shares)	$ 70.5