Deposits and Borrowings - Long-Term Debt (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 30,113	$ 24,439
Total short-term borrowings and long-term debt	42,243	40,654
Securitized debt obligations
Debt Instrument [Line Items]
Interest rate, minimum	0.20%
Interest rate, maximum	5.75%
Weighted average interest rate	1.35%
Long-term debt	10,508	10,289
Total senior and subordinated notes
Debt Instrument [Line Items]
Long-term debt	18,534	13,134
Senior notes | Total unsecured senior debt
Debt Instrument [Line Items]
Weighted average interest rate	2.66%
Long-term debt	15,935	10,464
Senior notes | Fixed unsecured senior debt
Debt Instrument [Line Items]
Interest rate, minimum	1.00%
Interest rate, maximum	6.75%
Weighted average interest rate	2.77%
Long-term debt	15,055	9,612
Senior notes | Floating unsecured senior debt
Debt Instrument [Line Items]
Interest rate, minimum	0.68%
Interest rate, maximum	0.88%
Weighted average interest rate	0.77%
Long-term debt	880	852
Subordinated notes | Fixed unsecured subordinated debt
Debt Instrument [Line Items]
Interest rate, minimum	3.38%
Interest rate, maximum	8.80%
Weighted average interest rate	4.97%
Long-term debt	2,599	2,670
FHLB advances
Debt Instrument [Line Items]
Interest rate, minimum	0.26%
Interest rate, maximum	6.88%
Weighted average interest rate	0.56%
Long-term debt	$ 1,071	$ 1,016