Borrowings - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Borrowings [Line Items]
Minimum contractual interest rates of long-term agreements to repurchase securities	3.65%	3.61%
Maximum contractual interest rates of long-term agreements to repurchase securities	4.58%	4.58%
Weighted-average contractual interest rates of long term agreements to repurchase securities	4.05%	4.00%
Repurchase dates of the long-term agreements outstanding	2020
Collateral posted	$ 1,100,000,000	$ 2,000,000,000
Trust preferred capital securities	0.00%	25.00%
Debt Maturity, Start Year	Jan. 01, 2027
Debt Maturity, End Year	Dec. 31, 2033
Minimum [Member]
Schedule Of Borrowings [Line Items]
Variable interest rate of Senior Notes /Junior Subordinated Debentures	1.74%	1.18%
Maximum [Member]
Schedule Of Borrowings [Line Items]
Variable interest rate of Senior Notes /Junior Subordinated Debentures	4.23%	3.67%
FHLBs Facility [Member]
Schedule Of Borrowings [Line Items]
Borrowing facilities available with FHLB's amount	$ 22,500,000,000
Federal Reserve Bank of New York [Member]
Schedule Of Borrowings [Line Items]
Line of credit facility	$ 11,200,000,000
Variable Rate Senior Notes [Member]
Schedule Of Borrowings [Line Items]
Weighted-average variable rates payable	1.22%	0.69%
Variable Rate Senior Notes [Member] | Minimum [Member]
Schedule Of Borrowings [Line Items]
Variable interest rate of Senior Notes /Junior Subordinated Debentures	1.18%	0.62%
Variable Rate Senior Notes [Member] | Maximum [Member]
Schedule Of Borrowings [Line Items]
Variable interest rate of Senior Notes /Junior Subordinated Debentures	1.26%	0.75%
Long-term Fixed Rate Advances From FHLB [Member]
Schedule Of Borrowings [Line Items]
Advances from the FHLB maturity date	2035
Long-term Fixed Rate Advances From FHLB [Member] | Minimum [Member]
Schedule Of Borrowings [Line Items]
Variable contractual interest rate of long-term debt	1.17%
Long-term Fixed Rate Advances From FHLB [Member] | Maximum [Member]
Schedule Of Borrowings [Line Items]
Variable contractual interest rate of long-term debt	7.32%
Long-term Fixed Rate Advances From FHLB [Member] | Weighted Average [Member]
Schedule Of Borrowings [Line Items]
Variable contractual interest rate of long-term debt	1.65%	1.66%
Subordinated Capital Notes [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	1.97%	1.64%
Subordinated Variable Rate Notes Due 2021 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	1.57%
Junior Subordinated Debt [Member]
Schedule Of Borrowings [Line Items]
Weighted-average variable rates payable	2.33%	1.78%