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Note Borrowings (Additional Information) (Detail) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Debt Disclosure [Line Items]    
Federal Home Loan Bank Advances General Debt Obligations Disclosures Amount Of Available Unused Funds $ 3,800 $ 3,900
Federal Home Loan Bank Advances And Letters Of Credit Amount Used 673 762
Federal Reserve Bank Advances    
Debt Disclosure [Line Items]    
Line Of Credit Facility Current Borrowing Capacity 1,200 $ 1,300
Line Of Credit Facility Capacity Available For Specific Purpose Other Than For Trade Purchases $ 200