Carrying Amounts and Fair Values of the Company's Financial Instruments (Detail) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Financial assets
Trading Securities	[1]	$ 5,112	$ 5,093
Available-for-sale Securities	[2],[3]	30,934	30,947	[4]
Loans Held-for-sale, Fair Value Disclosure		1,428	1,577
Other Assets, Fair Value Disclosure			56
Fair Value, Inputs, Level 1 [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		7,304	6,912
Trading Securities		485	608
Available-for-sale Securities		4,340	4,331
Loans Held-for-sale, Fair Value Disclosure		0	0
Loans Net Fair Value Disclosure		0	0
Other Assets, Fair Value Disclosure		143	56
Financial liabilities
Consumer And Commercial Deposits, Fair Value Disclosure		0	0
Short-term Debt, Fair Value		0	0
Long-term Debt, Fair Value		0	0
Trading liabilities		841	769
Fair Value, Inputs, Level 2 [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Trading Securities		4,610	4,469
Available-for-sale Securities		26,594	26,544
Loans Held-for-sale, Fair Value Disclosure		2,348	2,239
Loans Net Fair Value Disclosure		0	0
Other Assets, Fair Value Disclosure		0	0
Financial liabilities
Consumer And Commercial Deposits, Fair Value Disclosure		13,478	11,906
Short-term Debt, Fair Value		3,572	4,781
Long-term Debt, Fair Value		9,631	8,834
Trading liabilities		880	498
Fair Value, Inputs, Level 3 [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Trading Securities		17	16
Available-for-sale Securities		0	72
Loans Held-for-sale, Fair Value Disclosure		41	54
Loans Net Fair Value Disclosure		141,174	141,575
Other Assets, Fair Value Disclosure		418	418
Financial liabilities
Consumer And Commercial Deposits, Fair Value Disclosure		0	0
Short-term Debt, Fair Value		0	0
Long-term Debt, Fair Value		1,112	1,058
Trading liabilities		16	16
Reported Value Measurement [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		7,304	6,912
Trading Securities		5,112	5,093
Available-for-sale Securities		30,934	30,947
Loans Held-for-sale, Fair Value Disclosure		2,377	2,290
Loans Net Fair Value Disclosure		140,924	141,446
Other Assets, Fair Value Disclosure		561	474
Financial liabilities
Consumer And Commercial Deposits, Fair Value Disclosure		13,715	12,076
Short-term Debt, Fair Value		3,572	4,781
Long-term Debt, Fair Value		10,692	9,785
Trading liabilities		1,737	1,283
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		7,304	6,912
Trading Securities		5,112	5,093
Available-for-sale Securities		30,934	30,947
Loans Held-for-sale, Fair Value Disclosure		2,389	2,293
Loans Net Fair Value Disclosure		141,174	141,575
Other Assets, Fair Value Disclosure		561	474
Financial liabilities
Consumer And Commercial Deposits, Fair Value Disclosure		13,478	11,906
Short-term Debt, Fair Value		3,572	4,781
Long-term Debt, Fair Value		10,743	9,892
Trading liabilities		$ 1,737	$ 1,283

[1] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,248 million and $1,086 million at March 31, 2018 and December 31, 2017, respectively.

[2] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $214 million and $223 million at March 31, 2018 and December 31, 2017, respectively.

[3] Text selection found with no content.

[4] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets on the Consolidated Balance Sheets. Reclassifications have been made to previously reported amounts for comparability. See Note 9, "Other Assets," for additional information.