Long-Term Borrowings - Subordinated Long-Term Borrowings (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total subordinated Long-term Borrowings, par amount	$ 16,187	$ 16,418
Long-term subordinated debt outstanding	17,280	17,604
Long-term junior subordinated debt	1,807	1,809
Total subordinated Long-term Borrowings	$ 19,087	$ 19,413
Effective weighted average interest rate of long-term subordinated debt, after hedging	4.29%	4.29%
Effective weighted average interest rate of long-term junior subordinated debt, after hedging	5.72%	5.70%
Effective weighted average interest rate on long-term subordinated borrowings, after hedging	4.41%	4.41%
Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, par amount	$ 14,827	$ 15,058
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, par amount	$ 1,360	$ 1,360