Carrying Amounts and Fair Values of the Company's Financial Instruments (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Dec. 31, 2015
Document Period End Date		Mar. 31, 2016
Financial assets
Trading assets	[1]	$ 7,050	$ 6,119
Available-for-sale Securities		28,188	27,825
Loans Held-for-sale, Fair Value Disclosure		1,593	1,494
Financial liabilities
Long-term Debt, Fair Value		975	973
Trading liabilities		1,536	1,263
Reported Value Measurement [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure	[2]	4,327	5,599
Trading assets	[3]	7,050	6,119
Available-for-sale Securities	[3]	28,188	27,825
Loans Held-for-sale, Fair Value Disclosure	[4]	1,911	1,838
Loans Net Fair Value Disclosure	[5]	137,976	134,690
Financial liabilities
Consumer And Commercial Deposits, Fair Value Disclosure	[6]	152,161	149,830
Short-term Debt, Fair Value	[7]	4,944	4,627
Long-term Debt, Fair Value	[7]	8,514	8,462
Trading liabilities	[3]	1,536	1,263
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Trading assets		1,046	866
Available-for-sale Securities		3,844	3,542
Financial liabilities
Long-term Debt, Fair Value		0	0
Trading liabilities		717	664
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial assets
Trading assets		10,058	8,456
Available-for-sale Securities		23,764	23,727
Financial liabilities
Long-term Debt, Fair Value		975	973
Trading liabilities		5,571	4,557
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Trading assets		37	110
Available-for-sale Securities		580	556
Financial liabilities
Long-term Debt, Fair Value		0	0
Trading liabilities		5	6
Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Trading assets		0	0
Available-for-sale Securities		0	0
Financial liabilities
Trading liabilities		0	0
Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Inputs, Level 2 [Member]
Financial assets
Trading assets		686	553
Available-for-sale Securities		23,190	23,124
Financial liabilities
Trading liabilities		3	37
Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Trading assets		0	0
Available-for-sale Securities		0	0
Financial liabilities
Trading liabilities		$ 0	$ 0

[1] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,484 million and $1,377 million at March 31, 2016 and December 31, 2015, respectively

[2] Cash and cash equivalents are valued at their carrying amounts, which are reasonable estimates of fair value due to the relatively short period to maturity of the instruments.

[3] Trading assets and derivative instruments, securities AFS, and trading liabilities and derivative instruments that are classified as level 1 are valued based on quoted market prices. For those instruments classified as level 2 or 3, refer to the respective valuation discussions within this footn

[4] LHFS are generally valued based on observable current market prices or, if quoted market prices are not available, quoted market prices of similar instruments. Refer to the LHFS section within this footnote for further discussion. When valuation assumptions are not readily observable in the market, instruments are valued based on the best available data to approximate fair value. This data may be internally developed and considers risk premiums that a market participant would require under then-current market conditions.

[5] LHFI fair values are based on a hypothetical exit price, which does not represent the estimated intrinsic value of the loan if held for investment. The assumptions used are expected to approximate those that a market participant purchasing the loans would use to value the loans, including a market risk premium and liquidity discount. Estimating the fair value of the loan portfolio when loan sales and trading markets are illiquid or nonexistent requires significant judgment.Generally, the Company measures fair value for LHFI based on estimated future discounted cash flows using current origination rates for loans with similar terms and credit quality, which derived an estimated value of 102% and 101% on the loan portfolio’s net carrying value at March 31, 2016 and December 31, 2015, respectively. The value derived from origination rates likely does not represent an exit price; therefore, an incremental market risk and liquidity discount was applied when estimating the fair value of these loans. The discounted value is a function of a market participant’s required yield in the current environment and is not a reflection of the expected cumulative losses on the loans.

[6] Deposit liabilities with no defined maturity such as DDAs, NOW/money market accounts, and savings accounts have a fair value equal to the amount payable on demand at the reporting date (i.e., their carrying amounts). Fair values for CDs are estimated using a discounted cash flow approach that applies current interest rates to a schedule of aggregated expected maturities. The assumptions used in the discounted cash flow analysis are expected to approximate those that market participants would use in valuing deposits. The value of long-term relationships with depositors is not taken into account in estimating fair values

[7] Fair values for short-term borrowings and certain long-term debt are based on quoted market prices for similar instruments or estimated discounted cash flows utilizing the Company’s current incremental borrowing rate for similar types of instruments. For long-term debt that the Company measures at fair value, refer to the respective valuation section within this footnote. For level 3 debt, the terms are unique in nature or there are no similar instruments that can be used to value the instrument without using significant unobservable assumptions. In these situations, the Company reviews current borrowing rates along with the collateral levels that secure the debt in determining an appropriate fair value adjustment.