Borrowings - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Borrowings [Line Items]
Minimum variable interest rate of Senior Notes /Junior Subordinated Debentures	1.18%	1.08%
Maximum variable interest rate of Senior Notes /Junior Subordinated Debentures	3.67%	3.58%
Minimum contractual interest rates of long-term agreements to repurchase securities	3.61%	3.61%
Maximum contractual interest rates of long-term agreements to repurchase securities	4.58%	4.30%
Weighted-average contractual interest rates of long term agreements to repurchase securities	4.00%	3.90%
Repurchase dates of the long-term agreements outstanding	2020
Trust preferred capital securities	25.00%
Interest rate payable on Junior Subordinated Debentures	1.78%	1.66%
Debt Maturity, Start Year	Jan. 01, 2027
Debt Maturity, End Year	Dec. 31, 2033
Government Issued or Guaranteed [Member]
Schedule Of Borrowings [Line Items]
Collateralized Financings	$ 2,000	$ 1,500
FHLBs Facility [Member]
Schedule Of Borrowings [Line Items]
Borrowing facilities available with FHLB's amount	20,500
Federal Reserve Bank of New York [Member]
Schedule Of Borrowings [Line Items]
Line of credit facility	$ 11,900
Variable Rate Senior Notes [Member]
Schedule Of Borrowings [Line Items]
Minimum variable interest rate of Senior Notes /Junior Subordinated Debentures	0.62%	0.54%
Maximum variable interest rate of Senior Notes /Junior Subordinated Debentures	0.75%	0.61%
Weighted-average contractual interest rate payable	0.69%	0.56%
Long-term Fixed Rate Advances From FHLB [Member]
Schedule Of Borrowings [Line Items]
Variable contractual interest rate of long-term debt lower limit	1.17%
Variable contractual interest rate of long-term debt upper limit	7.32%
Weighted-average contractual variable interest rate	1.66%	1.68%
Advances from the FHLB maturity date	2035
Junior Subordinated Debt [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures redeemed	$ 323
Subordinated Capital Notes [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	1.64%