Long-Term Borrowings - Subordinated Long-Term Borrowings (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total subordinated Long-term Borrowings, par amount	$ 16,544	$ 19,363
Long-term subordinated debt outstanding	18,290	20,784
Long-term junior subordinated debt	1,811	1,817
Total subordinated Long-term Borrowings	$ 20,101	$ 22,601
Effective weighted average interest rate of long-term subordinated debt, after hedging	4.27%	3.79%
Effective weighted average interest rate of long-term junior subordinated debt, after hedging	5.79%	5.77%
Effective weighted average interest rate on long-term subordinated borrowings, after hedging	4.39%	3.93%
Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, par amount	$ 15,184	$ 18,004
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, par amount	$ 1,360	$ 1,359