Summary of Carrying Values, Estimated Fair Values and Fair Value Measurement Levels of Financial Instruments (Detail) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Financial Assets:
Cash and cash equivalents		$ 1,228,295	$ 1,474,955	$ 2,528,169
FHLB stock		582,348	644,590
Loans and leases, net		40,725,589	40,006,088
Financial Liabilities:
Deposits		32,332,526	30,764,430
Borrowed funds		13,082,138	14,207,866
Financial Assets:
Cash and cash equivalents		1,228,295	1,474,955
FHLB stock	[1]	582,348	644,590
Loans and leases, net		40,523,888	39,461,985
Financial Liabilities:
Deposits		32,392,499	30,748,729
Borrowed funds		13,242,632	14,136,526
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and cash equivalents		1,228,295	1,474,955
Financial Liabilities:
Deposits	[2]	18,046,240	18,570,108
Significant Other Observable Inputs (Level 2)
Financial Assets:
FHLB stock	[1]	582,348	644,590
Financial Liabilities:
Deposits	[3]	14,346,259	12,178,621
Borrowed funds		13,242,632	14,136,526
Significant Unobservable Inputs (Level 3)
Financial Assets:
Loans and leases, net		$ 40,523,888	$ 39,461,985

[1] Carrying value and estimated fair value are at cost.

[2] Interest-bearing checking and money market accounts, savings accounts, and non-interest-bearing accounts.

[3] Certificates of deposit.