Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Jun. 30, 2017 USD ($) segment point derivative_instrument
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loan portfolio segments | segment	2
Average FICO credit score of borrower (in points) | point	740
Loan to value percentage, less than	90.00%
Nonperforming assets, period past due	90 days
Threshold period after bankruptcy notification for charge-off	60 days
Threshold period after bankruptcy notification past due	120 days
Employee stock ownership plan, requisite service for eligibility	1000 hours
Employee stock ownership plan, period for eligibility	12 months
Employee stock ownership plan, minimum age for eligibility	21 years
Employee stock ownership plan, contribution period for loan payable	20 years
Derivative, number of instruments held | derivative_instrument	2
Core Deposits | Minimum
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finite-lived intangible asset, useful life	5 years
Core Deposits | Maximum
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finite-lived intangible asset, useful life	10 years
Retail Consumer loans | Uncollateralized
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold period past due for charge-off	90 days
Retail Consumer loans | Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold period past due for charge-off	120 days
Commercial Paper
Financing Receivable, Recorded Investment, Past Due [Line Items]
Maturities of short-term debt of investment graded corporations (less than)	270 days
Maximum amount of instruments per issuer | $	$ 10,000,000.0