Contractual Maturities of Outstanding Federal Home Loan Bank Advances (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Year of Maturity
2018	$ 0	$ 300,000,000,000
Total FHLB advances	12,104,500,000	$ 11,664,500,000
Contractual Maturity
Year of Maturity
2018	3,923,500,000
2019	4,431,000,000
2020	3,150,000,000
2021	600,000,000
Total FHLB advances	$ 12,104,500,000
Weighted Average Interest Rate
2018	1.51%
2019	1.74%
2020	2.09%
2021	2.21%
Total FHLB advances	1.78%