Note Borrowings (Additional Information) (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Debt Disclosure [Line Items]
Federal Home Loan Bank Advances General Debt Obligations Disclosures Amount Of Available Unused Funds	$ 4,100	$ 3,900
Federal Home Loan Bank Advances And Letters Of Credit Amount Used	922	762
Pledged Financial Instruments Not Separately Reported Loans For Letter Of Credit Facilities	240
Federal Reserve Bank Advances
Debt Disclosure [Line Items]
Line Of Credit Facility Current Borrowing Capacity	$ 1,300	$ 1,300