Weighted Average Interest Rates for Each Type of Deposit (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amount
Interest-bearing checking and money market accounts	$ 12,936,301	$ 13,395,080
Savings accounts	5,210,001	5,280,374
Certificates of deposit	8,643,646	7,577,170
Non-interest-bearing accounts	2,312,215	2,635,279
Total deposits	$ 29,102,163	$ 28,887,903
Percent of Total
Interest-bearing checking and money market accounts	44.45%	46.37%
Savings accounts	17.90%	18.28%
Certificates of deposit	29.70%	26.23%
Non-interest-bearing accounts	7.95%	9.12%
Total deposits	100.00%	100.00%
Weighted Average Interest Rate
Interest-bearing checking and money market accounts, weighted average interest rate	0.23%	0.55%
Savings accounts, weighted average interest rate	0.52%	0.46%
Certificates of deposit, weighted average interest rate	1.31%	1.12%
Non-interest-bearing accounts, weighted average interest rate	0.00%	0.00%
Total deposits, weighted average interest rate	0.58%	0.63%