Netting Arrangements for Certain Financial Instruments and Securities Financing Activities - Summary of Maturities by Category of Collateral Pledged for Repurchase Agreements (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross amount of recognized liabilities	$ 1,017	$ 1,092
U.S. Treasury and Agencies [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross amount of recognized liabilities	88	122
Mortgage-Backed Securities Residential [Member] | Agency [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross amount of recognized liabilities	929	970
Overnight and Continuous [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross amount of recognized liabilities	955	924
Overnight and Continuous [Member] | U.S. Treasury and Agencies [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross amount of recognized liabilities	88	122
Overnight and Continuous [Member] | Mortgage-Backed Securities Residential [Member] | Agency [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross amount of recognized liabilities	867	802
Less Than 30 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross amount of recognized liabilities	62	168
Less Than 30 Days [Member] | Mortgage-Backed Securities Residential [Member] | Agency [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross amount of recognized liabilities	$ 62	$ 168